diff --git a/DATA_REQUIREMENTS.md b/DATA_REQUIREMENTS.md
new file mode 100644
index 0000000..9746d7e
--- /dev/null
+++ b/DATA_REQUIREMENTS.md
@@ -0,0 +1,55 @@
+# Country Data Requirements
+Guide for adding a new country to the static Region Identifier dataset. Each supported country needs three JSON files plus a small code change.
+
+## 1) Country config – `country/ISO3.json`
+- Keys:
+  - `zipCodeFormat`: `"numeric"` or `"alpha"`.
+  - `zipCodeLength`: integer, required for numeric formats to pad/compare values (USA=5, AUS=4, DEU=5, etc.). Omit for alpha formats (CAN/GBR/NLD).
+- Example:
+```json
+{ "zipCodeFormat": "numeric", "zipCodeLength": 5 }
+```
+
+## 2) Region names – `regionNames/ISO3.json`
+- Plain object mapping ISO 3166-2 region codes (same codes used in `regions/*.json`) to display names in English.
+- Example (`regionNames/AUS.json`):
+```json
+{
+  "AU-NSW": "New South Wales",
+  "AU-VIC": "Victoria"
+}
+```
+
+## 3) Region mappings – `regions/ISO3.json`
+Array of objects that map postal codes to ISO 3166-2 region codes. Formats already used in the repo:
+- **Numeric intervals** (inclusive): objects with `low`, `high`, `region`. Values can be numbers or numeric strings if leading zeros matter. Example (`regions/AUS.json`):
+```json
+{ "region": "AU-NSW", "low": 1000, "high": 1999 }
+```
+- **Explicit codes**: objects with `low`, `region`, no `high`. Every postal code (or prefix) must be listed. Use strings to preserve zeros. Examples:
+  - Belgium lists every 4-digit code (`regions/BEL.json`).
+  - Spain lists 5-digit codes as strings (`regions/ESP.json`).
+  - Mexico lists 2-digit prefixes (`regions/MEX.json`).
+  - CAN/GBR use alpha prefixes (e.g., `"low": "X0A"` or `"low": "AB"`).
+- **Discrete lists**: objects with `region` and `list` (array of codes). Numeric countries store numbers; matching uses `zipCodeLength` to pad leading zeros before comparison. Examples: USA (`list` of 5-digit numbers), RUS (per-region lists).
+
+Additional format notes:
+- Files can mix formats if needed. Order matters because the lookup stops at the first match.
+- Intervals and lists are treated as inclusive ranges; for alpha codes only exact equality is used.
+- Keep codes as strings when leading zeros are significant.
+
+## 4) Code wiring
+- Add the ISO3 code to `availableCountries` in `lib/region.js`; otherwise the static data is ignored and Google is used.
+- If the country needs custom postal-code normalization, extend `validateZipCode` (see existing cases for GBR, CAN, NLD, MEX).
+
+## 5) Testing
+- Add test cases to `test/tests.js` under `countriesPostalCodes`: include the country ISO/name, a representative zip, expected region code, and set `usingGoogle: false`.
+- Run `npm test` to execute Mocha tests.
+- Optional: verify pretty-name lookups via `getNameFromCountryAndRegion` using the `regionNames` file.
+
+## 6) Data quality checklist
+- Region codes must be valid ISO 3166-2 for the country.
+- `regionNames` should be English and cover every region code present in `regions/ISO3.json`.
+- Postal-code coverage should include territories and edge prefixes (e.g., US territories, Canadian northern prefixes).
+- Prefer ascending ordering of `regions` entries to keep matching predictable.
+- Avoid empty mappings; placeholders (e.g., empty lists) will yield null regions and fall back to Google.
diff --git a/README.md b/README.md
index b8c236a..cc03d24 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,7 @@ Utility module that provides an easy way to identify the region of the country d
 - MEX
 - NLD
 - RUS
+- SRB
 - SWE
 - USA
 
diff --git a/country/SRB.json b/country/SRB.json
new file mode 100644
index 0000000..797c859
--- /dev/null
+++ b/country/SRB.json
@@ -0,0 +1,4 @@
+{
+  "zipCodeFormat": "numeric",
+  "zipCodeLength": 5
+}
diff --git a/lib/region.js b/lib/region.js
index 1940c00..6f9599f 100644
--- a/lib/region.js
+++ b/lib/region.js
@@ -18,6 +18,7 @@ const availableCountries = new Set([
   'MEX',
   'NLD',
   'RUS',
+  'SRB',
   'SWE',
   'USA',
   'AUS',
diff --git a/regionNames/SRB.json b/regionNames/SRB.json
new file mode 100644
index 0000000..732ca2c
--- /dev/null
+++ b/regionNames/SRB.json
@@ -0,0 +1,27 @@
+{
+  "RS-00": "Belgrade",
+  "RS-01": "North Bačka",
+  "RS-02": "Central Banat",
+  "RS-03": "North Banat",
+  "RS-04": "South Banat",
+  "RS-05": "West Bačka",
+  "RS-06": "South Bačka",
+  "RS-07": "Srem",
+  "RS-08": "Mačva",
+  "RS-09": "Kolubara",
+  "RS-10": "Podunavlje",
+  "RS-11": "Braničevo",
+  "RS-12": "Šumadija",
+  "RS-13": "Pomoravlje",
+  "RS-14": "Bor",
+  "RS-15": "Zaječar",
+  "RS-16": "Zlatibor",
+  "RS-17": "Moravica",
+  "RS-18": "Raška",
+  "RS-19": "Rasina",
+  "RS-20": "Nišava",
+  "RS-21": "Toplica",
+  "RS-22": "Pirot",
+  "RS-23": "Jablanica",
+  "RS-24": "Pčinja"
+}
diff --git a/regions/SRB.json b/regions/SRB.json
new file mode 100644
index 0000000..eb8bd6c
--- /dev/null
+++ b/regions/SRB.json
@@ -0,0 +1,245 @@
+[
+  {
+    "region": "RS-00",
+    "low": 11000,
+    "high": 11299
+  },
+  {
+    "region": "RS-00",
+    "list": [
+      11306,
+      11307,
+      11308,
+      11309,
+      11351
+    ]
+  },
+  {
+    "region": "RS-10",
+    "low": 11300,
+    "high": 11305
+  },
+  {
+    "region": "RS-10",
+    "low": 11310,
+    "high": 11325
+  },
+  {
+    "region": "RS-10",
+    "low": 11328,
+    "high": 11329
+  },
+  {
+    "region": "RS-10",
+    "list": [
+      11420,
+      11423,
+      11425,
+      11431,
+      11432
+    ]
+  },
+  {
+    "region": "RS-00",
+    "low": 11400,
+    "high": 11419
+  },
+  {
+    "region": "RS-00",
+    "low": 11426,
+    "high": 11427
+  },
+  {
+    "region": "RS-00",
+    "list": [
+      11430,
+      11433
+    ]
+  },
+  {
+    "region": "RS-00",
+    "low": 11450,
+    "high": 11462
+  },
+  {
+    "region": "RS-00",
+    "low": 11500,
+    "high": 11599
+  },
+  {
+    "region": "RS-02",
+    "list": [
+      11467
+    ]
+  },
+  {
+    "region": "RS-11",
+    "low": 12000,
+    "high": 12399
+  },
+  {
+    "region": "RS-09",
+    "low": 14000,
+    "high": 14299
+  },
+  {
+    "region": "RS-08",
+    "low": 15000,
+    "high": 15399
+  },
+  {
+    "region": "RS-23",
+    "low": 16000,
+    "high": 16299
+  },
+  {
+    "region": "RS-24",
+    "low": 17500,
+    "high": 17599
+  },
+  {
+    "region": "RS-15",
+    "low": 18230,
+    "high": 18237
+  },
+  {
+    "region": "RS-20",
+    "low": 18000,
+    "high": 18229
+  },
+  {
+    "region": "RS-20",
+    "low": 18238,
+    "high": 18269
+  },
+  {
+    "region": "RS-22",
+    "low": 18300,
+    "high": 18359
+  },
+  {
+    "region": "RS-20",
+    "low": 18360,
+    "high": 18369
+  },
+  {
+    "region": "RS-21",
+    "low": 18400,
+    "high": 18499
+  },
+  {
+    "region": "RS-15",
+    "low": 19000,
+    "high": 19099
+  },
+  {
+    "region": "RS-15",
+    "low": 19200,
+    "high": 19209
+  },
+  {
+    "region": "RS-15",
+    "low": 19214,
+    "high": 19214
+  },
+  {
+    "region": "RS-15",
+    "low": 19227,
+    "high": 19228
+  },
+  {
+    "region": "RS-14",
+    "low": 19210,
+    "high": 19229
+  },
+  {
+    "region": "RS-15",
+    "low": 19233,
+    "high": 19235
+  },
+  {
+    "region": "RS-14",
+    "low": 19250,
+    "high": 19259
+  },
+  {
+    "region": "RS-14",
+    "low": 19300,
+    "high": 19335
+  },
+  {
+    "region": "RS-15",
+    "low": 19340,
+    "high": 19378
+  },
+  {
+    "region": "RS-06",
+    "low": 21000,
+    "high": 21499
+  },
+  {
+    "region": "RS-07",
+    "low": 22000,
+    "high": 22499
+  },
+  {
+    "region": "RS-02",
+    "low": 23100,
+    "high": 23299
+  },
+  {
+    "region": "RS-03",
+    "low": 23300,
+    "high": 23399
+  },
+  {
+    "region": "RS-01",
+    "low": 24000,
+    "high": 24399
+  },
+  {
+    "region": "RS-03",
+    "low": 24400,
+    "high": 24499
+  },
+  {
+    "region": "RS-05",
+    "low": 25000,
+    "high": 25299
+  },
+  {
+    "region": "RS-04",
+    "low": 26000,
+    "high": 26399
+  },
+  {
+    "region": "RS-16",
+    "low": 31000,
+    "high": 31399
+  },
+  {
+    "region": "RS-17",
+    "low": 32000,
+    "high": 32399
+  },
+  {
+    "region": "RS-12",
+    "low": 34000,
+    "high": 34399
+  },
+  {
+    "region": "RS-13",
+    "low": 35000,
+    "high": 35299
+  },
+  {
+    "region": "RS-18",
+    "low": 36000,
+    "high": 36399
+  },
+  {
+    "region": "RS-19",
+    "low": 37000,
+    "high": 37299
+  }
+]
\ No newline at end of file
diff --git a/test/tests.js b/test/tests.js
index 007dd31..02572f2 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -206,6 +206,27 @@ const countriesPostalCodes = {
     result: 'MX-CMX',
     usingGoogle: false,
   }],
+  'Serbia': [{
+    name: 'SRB',
+    zip: '11000',
+    result: 'RS-00',
+    usingGoogle: false,
+  }, {
+    name: 'SRB',
+    zip: '11320',
+    result: 'RS-10',
+    usingGoogle: false,
+  }, {
+    name: 'SRB',
+    zip: '18230',
+    result: 'RS-15',
+    usingGoogle: false,
+  }, {
+    name: 'SRB',
+    zip: '24430',
+    result: 'RS-03',
+    usingGoogle: false,
+  }],
   'United States': [{
     name: 'USA',
     zip: '972022239',