diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3fec32c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+tmp/
diff --git a/.rspec b/.rspec
new file mode 100644
index 0000000..b83d9b7
--- /dev/null
+++ b/.rspec
@@ -0,0 +1,3 @@
+--color
+--format documentation
+--require spec_helper
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..851fabc
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,2 @@
+source 'https://rubygems.org'
+gemspec
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..c9bd8d1
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,45 @@
+PATH
+  remote: .
+  specs:
+    sudoku_validator (0.0.1)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    aruba (0.5.3)
+      childprocess (>= 0.3.6)
+      cucumber (>= 1.1.1)
+      rspec-expectations (>= 2.7.0)
+    builder (3.2.2)
+    childprocess (0.3.9)
+      ffi (~> 1.0, >= 1.0.11)
+    cucumber (1.3.10)
+      builder (>= 2.1.2)
+      diff-lcs (>= 1.1.3)
+      gherkin (~> 2.12)
+      multi_json (>= 1.7.5, < 2.0)
+      multi_test (>= 0.0.2)
+    diff-lcs (1.2.5)
+    ffi (1.9.3)
+    gherkin (2.12.2)
+      multi_json (~> 1.3)
+    multi_json (1.8.2)
+    multi_test (0.0.2)
+    rake (10.1.0)
+    rspec (2.14.1)
+      rspec-core (~> 2.14.0)
+      rspec-expectations (~> 2.14.0)
+      rspec-mocks (~> 2.14.0)
+    rspec-core (2.14.7)
+    rspec-expectations (2.14.4)
+      diff-lcs (>= 1.1.3, < 2.0)
+    rspec-mocks (2.14.4)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  aruba
+  rake
+  rspec
+  sudoku_validator!
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..c92204b
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,9 @@
+require 'cucumber'
+require 'cucumber/rake/task'
+
+Cucumber::Rake::Task.new(:features) do |t|
+  t.cucumber_opts = "features --format pretty -x"
+  t.fork = false
+end
+
+task :default => :features
diff --git a/bin/sudoku-validator b/bin/sudoku-validator
new file mode 100755
index 0000000..e884ffe
--- /dev/null
+++ b/bin/sudoku-validator
@@ -0,0 +1,24 @@
+#!/usr/bin/env ruby
+
+require_relative '../lib/sudoku_fileparser'
+require_relative '../lib/sudoku_puzzle'
+require_relative '../lib/sudoku_validator'
+
+exit unless filename = ARGV[0]
+
+filepath = File.expand_path(filename)
+if File.exist?(filepath)
+  parser    = Sudoku::FileParser.new(File.read(filepath))
+  puzzle    = Sudoku::Puzzle.new(parser.parse_rows)
+  validator = Sudoku::Validator.new(puzzle)
+
+  puts validator.status
+  if validator.errors.any?
+    puts "Errors:"
+    validator.errors.each.with_index(1) do |error, index|
+      puts "  #{index}) #{error}"
+    end
+  end
+else
+  puts "Could not find file #{filename}"
+end
diff --git a/features/sudoku_validator.feature b/features/sudoku_validator.feature
new file mode 100644
index 0000000..59496b1
--- /dev/null
+++ b/features/sudoku_validator.feature
@@ -0,0 +1,23 @@
+Feature: Validating .sudoku files
+
+  Scenario: A valid, complete sudoku
+    When I successfully run `sudoku-validator ./valid_complete.sudoku`
+    Then the output should contain "This sudoku is valid."
+    Then the output should not contain "Errors:"
+
+  Scenario: A valid, incomplete sudoku
+    When I successfully run `sudoku-validator ./valid_incomplete.sudoku`
+    Then the output should contain "This sudoku is valid, but incomplete."
+    Then the output should not contain "Errors:"
+
+  Scenario: An invalid, complete sudoku
+    When I successfully run `sudoku-validator ./invalid_complete.sudoku`
+    Then the output should contain "This sudoku is invalid."
+    Then the output should contain "Column 4 contains a duplicate 8 in squares 2 and 5"
+    Then the output should contain "Column 6 contains a duplicate 2 in squares 1 and 5"
+
+  Scenario: An invalid, incomplete sudoku
+    When I successfully run `sudoku-validator ./invalid_incomplete.sudoku`
+    Then the output should contain "This sudoku is invalid."
+    Then the output should contain "Column 2 contains a duplicate 5 in squares 1 and 7"
+    Then the output should contain "Column 5 contains a duplicate 8 in squares 2 and 7"
diff --git a/features/support/env.rb b/features/support/env.rb
new file mode 100644
index 0000000..e52a59f
--- /dev/null
+++ b/features/support/env.rb
@@ -0,0 +1,5 @@
+require 'aruba/cucumber'
+
+Before do
+  @dirs = ["."]
+end
diff --git a/lib/sudoku_fileparser.rb b/lib/sudoku_fileparser.rb
new file mode 100644
index 0000000..9322abc
--- /dev/null
+++ b/lib/sudoku_fileparser.rb
@@ -0,0 +1,28 @@
+module Sudoku
+  class FileParser
+    def initialize(file = nil)
+      raise(ArgumentError, "A file is required.") if file.nil?
+      @file = file
+    end
+
+    def parse_rows
+      @file.strip.each_line.map do |line|
+        parse_line(line) unless separator?(line)
+      end.compact
+    end
+
+    private
+
+    def parse_line(line)
+      parse_empties(line).split(/[^\d]+/).map(&:to_i)
+    end
+
+    def parse_empties(line)
+      line.gsub(".", "0")
+    end
+
+    def separator?(line)
+      line.start_with?('-')
+    end
+  end
+end
diff --git a/lib/sudoku_puzzle.rb b/lib/sudoku_puzzle.rb
new file mode 100644
index 0000000..795f14a
--- /dev/null
+++ b/lib/sudoku_puzzle.rb
@@ -0,0 +1,57 @@
+require_relative 'sudoku_unit'
+require 'matrix'
+
+module Sudoku
+  class Puzzle
+    def initialize(rows = [])
+      raise(ArgumentError, "An array of rows is required to create a puzzle.") if rows.empty?
+      @grid = create_grid(rows)
+    end
+
+    def rows
+      Hash[@grid.row_vectors.map.with_index(1) do |row, index|
+        [index, Row[*row]]
+      end]
+    end
+
+    def columns
+      Hash[@grid.column_vectors.map.with_index(1) do |column, index|
+        [index, Column[*column]]
+      end]
+    end
+
+    def boxes
+      Hash[[0, 3, 6].repeated_permutation(2).map.with_index(1) do |(x, y), index|
+        [index, Box[*@grid.minor(x, 3,  y, 3).to_a.flatten]]
+      end]
+    end
+
+    def complete?
+      rows.all? { |index, row| row.complete? }
+    end
+
+    def valid?
+      all_units.all?(&:valid?)
+    end
+
+    def eql?(other)
+      hash == other.hash
+    end
+
+    def hash
+      @grid.hash
+    end
+
+    alias_method :==, :eql?
+
+    private
+
+    def create_grid(input_rows)
+      Matrix[*input_rows]
+    end
+
+    def all_units
+      rows.values + columns.values + boxes.values
+    end
+  end
+end
diff --git a/lib/sudoku_unit.rb b/lib/sudoku_unit.rb
new file mode 100644
index 0000000..07e5ebf
--- /dev/null
+++ b/lib/sudoku_unit.rb
@@ -0,0 +1,59 @@
+module Sudoku
+  class Unit
+    def self.[](*values)
+      new(values)
+    end
+
+    def initialize(values)
+      @squares = values
+    end
+
+    def positions
+      @squares.each.with_index(1).inject ({}) do |h, (number, position)|
+        h.tap { |h| h[number] = h[number] ? [h[number]].flatten << position : position }
+      end
+    end
+
+    def valid?
+      non_empty_squares.uniq.count === non_empty_squares.count
+    end
+
+    def complete?
+      @squares.none?(&:zero?)
+    end
+
+    def eql?(other)
+      self.class == other.class && hash == other.hash
+    end
+
+    def hash
+      @squares.hash
+    end
+
+    alias_method :==, :eql?
+
+    private
+
+    def non_empty_squares
+      @squares.reject(&:zero?)
+    end
+  end
+
+  class Row < Unit
+    def type
+      "Row"
+    end
+  end
+
+  class Column < Unit
+    def type
+      "Column"
+    end
+  end
+
+  class Box < Unit
+    def type
+      "Box"
+    end
+  end
+end
diff --git a/lib/sudoku_validator.rb b/lib/sudoku_validator.rb
new file mode 100644
index 0000000..04327cb
--- /dev/null
+++ b/lib/sudoku_validator.rb
@@ -0,0 +1,59 @@
+module Sudoku
+  class Validator
+    attr_reader :puzzle
+
+    def initialize(puzzle = nil)
+      raise(ArgumentError, "A Puzzle is required.") if puzzle.nil?
+      @puzzle = puzzle
+    end
+
+    def status
+      case [puzzle.valid?, puzzle.complete?]
+      when [true, true]  then "This sudoku is valid."
+      when [true, false] then "This sudoku is valid, but incomplete."
+
+      else "This sudoku is invalid."
+      end
+    end
+
+    def errors
+      return [] if puzzle.valid?
+
+      [:rows, :columns, :boxes].map do |message|
+        puzzle.send(message).map do |index, unit|
+          duplicates(unit).map do |number, positions|
+            DuplicateError.new(unit.type, index, number, positions)
+          end
+        end
+      end.flatten
+    end
+
+    private
+
+    def duplicates(unit)
+      unit.positions.select do |number, position|
+        non_empty?(number) && duplicate?(position)
+      end
+    end
+
+    def non_empty?(number)
+      number != 0
+    end
+
+    def duplicate?(position)
+      position.is_a?(Array)
+    end
+  end
+
+  class DuplicateError < Struct.new(:type, :index, :number, :positions)
+    def to_s
+      "#{type} #{index} contains a duplicate #{number} in squares #{list(positions)}"
+    end
+
+    private
+
+    def list(positions)
+      "#{positions[0...-1].join(', ')} and #{positions.last}"
+    end
+  end
+end
diff --git a/spec/lib/sudoku_fileparser_spec.rb b/spec/lib/sudoku_fileparser_spec.rb
new file mode 100644
index 0000000..7ff6451
--- /dev/null
+++ b/spec/lib/sudoku_fileparser_spec.rb
@@ -0,0 +1,40 @@
+require 'sudoku_fileparser'
+
+module Sudoku
+  describe FileParser do
+    it "throws an ArgumentError if instantiated without a file" do
+      expect { FileParser.new }.to raise_error(ArgumentError)
+    end
+
+    it "can parse rows out of the file into a simple array format (strings are converted to numbers)" do
+      parser = FileParser.new(example_file)
+      parser.parse_rows.should eq [
+        [0, 5, 9, 6, 1, 2, 4, 3, 0],
+        [7, 0, 3, 8, 5, 4, 1, 0, 9],
+        [1, 6, 0, 3, 7, 9, 0, 2, 8],
+        [9, 8, 6, 0, 4, 0, 3, 5, 2],
+        [3, 7, 5, 2, 0, 8, 9, 1, 4],
+        [2, 4, 1, 0, 9, 0, 7, 8, 6],
+        [4, 3, 0, 9, 8, 1, 0, 7, 5],
+        [6, 0, 7, 4, 2, 5, 8, 0, 3],
+        [0, 9, 8, 7, 3, 6, 2, 4, 0]
+      ]
+    end
+
+    def example_file
+    %Q{
+. 5 9 |6 1 2 |4 3 . 
+7 . 3 |8 5 4 |1 . 9 
+1 6 . |3 7 9 |. 2 8 
+------+------+------
+9 8 6 |. 4 . |3 5 2 
+3 7 5 |2 . 8 |9 1 4 
+2 4 1 |. 9 . |7 8 6 
+------+------+------
+4 3 . |9 8 1 |. 7 5 
+6 . 7 |4 2 5 |8 . 3 
+. 9 8 |7 3 6 |2 4 .
+    }
+    end
+  end
+end
diff --git a/spec/lib/sudoku_puzzle_spec.rb b/spec/lib/sudoku_puzzle_spec.rb
new file mode 100644
index 0000000..baca4f3
--- /dev/null
+++ b/spec/lib/sudoku_puzzle_spec.rb
@@ -0,0 +1,98 @@
+require 'sudoku_puzzle'
+
+module Sudoku
+  describe Puzzle do
+    it "throws an ArgumentError if not passed an array of rows" do
+      expect { Puzzle.new }.to raise_error(ArgumentError)
+    end
+
+    it "is a value object (two puzzles with the same numbers are equal)" do
+      p1 = Puzzle.new(input_rows)
+      p2 = Puzzle.new(input_rows)
+
+      expect(p1).to eq p2
+    end
+
+    describe ":rows" do
+      it "returns a hash of Row objects indexed" do
+        puzzle = Puzzle.new(input_rows)
+
+        expect(puzzle.rows.count).to eq 9
+        expect(puzzle.rows[1]).to eq Row[0, 5, 9, 6, 1, 2, 4, 3, 0]
+        expect(puzzle.rows[9]).to eq Row[0, 9, 8, 7, 3, 6, 2, 4, 0]
+      end
+    end
+
+    describe ":columns" do
+      it "returns an array of Column objects indexed" do
+        puzzle = Puzzle.new(input_rows)
+
+        expect(puzzle.columns.count).to eq 9
+        expect(puzzle.columns[2]).to eq Column[5, 0, 6, 8, 7, 4, 3, 0, 9]
+        expect(puzzle.columns[8]).to eq Column[3, 0, 2, 5, 1, 8, 7, 0, 4]
+      end
+    end
+
+    describe ":boxes" do
+      it "returns an array of Box objects indexed" do
+        puzzle = Puzzle.new(input_rows)
+
+        expect(puzzle.boxes.count).to eq 9
+        expect(puzzle.boxes[3]).to eq Box[4, 3, 0, 1, 0, 9, 0, 2, 8]
+        expect(puzzle.boxes[7]).to eq Box[4, 3, 0, 6, 0, 7, 0, 9, 8]
+      end
+    end
+
+    describe "completeness" do
+      specify "a puzzle is complete if all of its rows are complete" do
+        puzzle = Puzzle.new([[1, 2, 3], [4, 9, 8], [5, 7, 6]])
+        expect(puzzle).to be_complete
+      end
+
+      specify "a puzzle is incomplete if any of its rows are incomplete" do
+        puzzle = Puzzle.new(input_rows)
+        expect(puzzle).not_to be_complete
+      end
+    end
+
+    describe "validity" do
+      specify "a puzzle is invalid if any of its rows, columns or boxes are invalid" do
+        puzzle = Puzzle.new(input_rows)
+        expect(puzzle).not_to be_valid
+      end
+
+      specify "a puzzle is valid if all of its rows, columns and boxes are valid" do
+        puzzle = Puzzle.new(valid_incomplete)
+        expect(puzzle).to be_valid
+      end
+    end
+
+    def input_rows
+      [
+        [0, 5, 9, 6, 1, 2, 4, 3, 0],
+        [7, 0, 3, 8, 5, 1, 1, 0, 9],
+        [1, 6, 0, 3, 7, 9, 0, 2, 8],
+        [9, 8, 6, 0, 4, 0, 3, 5, 2],
+        [3, 7, 5, 2, 0, 8, 9, 1, 4],
+        [2, 4, 1, 0, 9, 0, 7, 8, 6],
+        [4, 3, 0, 9, 8, 1, 0, 7, 5],
+        [6, 0, 7, 4, 2, 5, 8, 0, 3],
+        [0, 9, 8, 7, 3, 6, 2, 4, 0]
+      ]
+    end
+
+    def valid_incomplete
+      [
+        [8, 5, 0, 0, 0, 2, 4, 0, 0],
+        [7, 2, 0, 0, 0, 0, 0, 0, 9],
+        [0, 0, 4, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 1, 0, 7, 0, 0, 2],
+        [3, 0, 5, 0, 0, 0, 9, 0, 0],
+        [0, 4, 0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 8, 0, 0, 7, 0],
+        [0, 1, 7, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 3, 6, 0, 4, 0]
+      ]
+    end
+  end
+end
diff --git a/spec/lib/sudoku_sudoku_validator_spec.rb b/spec/lib/sudoku_sudoku_validator_spec.rb
new file mode 100644
index 0000000..034aa6b
--- /dev/null
+++ b/spec/lib/sudoku_sudoku_validator_spec.rb
@@ -0,0 +1,68 @@
+require 'sudoku_validator'
+require 'sudoku_unit'
+
+module Sudoku
+  describe Validator do
+    it "throws an ArgumentError if a puzzle is not passed in" do
+      expect { Validator.new }.to raise_error(ArgumentError)
+    end
+
+    describe "status" do
+      it "returns 'This sudoku is valid.' if the puzzle is valid and complete" do
+        puzzle = double(:valid? => true, :complete? => true)
+        expect(Validator.new(puzzle).status).to eq "This sudoku is valid."
+      end
+
+      it "returns 'This sudoku is valid, but incomplete.' if the puzzle is valid, but incomplete" do
+        puzzle = double(:valid? => true, :complete? => false)
+        expect(Validator.new(puzzle).status).to eq "This sudoku is valid, but incomplete."
+      end
+
+      it "returns 'This sudoku is invalid.' if the puzzle is invalid, but complete." do
+        puzzle = double(:valid? => false, :complete? => true)
+        expect(Validator.new(puzzle).status).to eq "This sudoku is invalid."
+      end
+
+      it "returns 'This sudoku is invalid.' if the puzzle is invalid and incomplete." do
+        puzzle = double(:valid? => false, :complete? => false)
+        expect(Validator.new(puzzle).status).to eq "This sudoku is invalid."
+      end
+    end
+
+    describe "errors" do
+      context "a valid puzzle" do
+        specify "contains no errors" do
+          puzzle = double(:valid? => true, :complete? => false)
+          expect(Validator.new(puzzle).errors).to be_empty
+        end
+      end
+
+      context "an invalid puzzle" do
+        let(:puzzle) { double(:valid? => false, :complete? => false) }
+        let(:errors) { Validator.new(puzzle).errors.map(&:to_s) }
+
+        before(:each) do
+          [:rows, :columns, :boxes].each do |message|
+            allow(puzzle).to receive(message).and_return({})
+          end
+        end
+
+        it "returns an error for a unit that contains a duplicate number" do
+          puzzle.stub(:rows).and_return({ 1 => Row[1, 8, 2, 3, 4, 5, 6, 7, 8] })
+          expect(errors).to include "Row 1 contains a duplicate 8 in squares 2 and 9"
+        end
+
+        it "ignores duplicate 0s as they are empty squares" do
+          puzzle.stub(:columns).and_return({ 4 => Column[0, 1, 0, 2, 0, 3, 0, 4, 0] })
+          expect(errors).to be_empty
+        end
+
+        it "returns errors for a unit that contains multiple duplicate numbers" do
+          puzzle.stub(:boxes).and_return({ 7 => Box[2, 3, 1, 6, 2, 7, 3, 3, 0] })
+          expect(errors).to include "Box 7 contains a duplicate 2 in squares 1 and 5"
+          expect(errors).to include "Box 7 contains a duplicate 3 in squares 2, 7 and 8"
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/sudoku_unit_spec.rb b/spec/lib/sudoku_unit_spec.rb
new file mode 100644
index 0000000..f530d27
--- /dev/null
+++ b/spec/lib/sudoku_unit_spec.rb
@@ -0,0 +1,66 @@
+require 'sudoku_unit'
+
+shared_examples "a Unit" do |type|
+  context "completeness" do
+    specify "a unit is incomplete if it contains empty squares" do
+      expect(described_class[0, 5, 9, 6, 1, 2, 4, 3, 8]).not_to be_complete
+    end
+
+    specify "a unit is complete if all squares are filled in" do
+      expect(described_class[7, 5, 9, 6, 1, 2, 4, 3, 8]).to be_complete
+    end
+  end
+
+  context "validity" do
+    specify "a unit is invalid if it contains duplicates (excludes empty squares)" do
+      expect(described_class[0, 0, 9, 6, 1, 0, 9, 3, 8]).not_to be_valid
+    end
+
+    specify "a unit is valid if it contains no duplicates" do
+      expect(described_class[0, 0, 2, 6, 1, 0, 9, 3, 8]).to be_valid
+    end
+  end
+
+  describe "listing square values against their positions in the unit" do
+    specify ":positions can list empty squares" do
+      output = {
+        0 => 8, 1 => 5, 2 => 6,
+        4 => 7, 5 => 2, 6 => 4,
+        7 => 1, 8 => 9, 9 => 3
+      }
+      expect(described_class[7, 5, 9, 6, 1, 2, 4, 0, 8].positions).to eq output
+    end
+
+    specify ":positions can list duplicate squares as an array" do
+      output = {
+        0 => [6, 8], 1 => 5, 4 => 7, 5 => 2,
+        7 => [1, 4], 8 => 9, 9 => 3
+      }
+      expect(described_class[7, 5, 9, 7, 1, 0, 4, 0, 8].positions).to eq output
+    end
+  end
+
+  context "immutability (value objects)" do
+    specify "two units of the same class with the same values are equal" do
+      expect(described_class[7, 5, 9, 6, 1, 2, 4, 3, 8]).to eq described_class[7, 5, 9, 6, 1, 2, 4, 3, 8]
+    end
+  end
+
+  it "has the right type" do
+    expect(described_class[1, 2, 3, 4, 5, 6, 7, 8, 9].type).to eq type
+  end
+end
+
+module Sudoku
+  describe Row do
+    it_behaves_like "a Unit", "Row"
+  end
+
+  describe Column do
+    it_behaves_like "a Unit", "Column"
+  end
+
+  describe Box do
+    it_behaves_like "a Unit", "Box"
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..dbc4f1a
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,17 @@
+# This file was generated by the `rspec --init` command. Conventionally, all
+# specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
+# Require this file using `require "spec_helper"` to ensure that it is only
+# loaded once.
+#
+# See http://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  config.treat_symbols_as_metadata_keys_with_true_values = true
+  config.run_all_when_everything_filtered = true
+  config.filter_run :focus
+
+  # Run specs in random order to surface order dependencies. If you find an
+  # order dependency and want to debug it, you can fix the order by providing
+  # the seed, which is printed after each run.
+  #     --seed 1234
+  config.order = 'random'
+end
diff --git a/sudoku_validator.gemspec b/sudoku_validator.gemspec
new file mode 100644
index 0000000..a954cb4
--- /dev/null
+++ b/sudoku_validator.gemspec
@@ -0,0 +1,14 @@
+Gem::Specification.new do |s|
+  s.name    = 'sudoku_validator'
+  s.version = '0.0.1'
+  s.summary = 'Sudoku Validator exercise from Thoughtbot'
+  s.author  = 'Dan Scotton'
+  s.email   = 'danscotton@gmail.com'
+
+  s.add_development_dependency 'aruba'
+  s.add_development_dependency 'rake'
+  s.add_development_dependency 'rspec'
+
+  s.executables << 'sudoku-validator'
+  s.require_path = "lib"
+end