diff --git a/.changeset/famous-humans-tell.md b/.changeset/famous-humans-tell.md
new file mode 100644
index 0000000..1a19f0e
--- /dev/null
+++ b/.changeset/famous-humans-tell.md
@@ -0,0 +1,5 @@
+---
+"@obosbbl/validation": minor
+---
+
+initial release
diff --git a/README.md b/README.md
index ec19974..d0eab94 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@ This a monorepo of OBOS' open source frontend modules.
 ## Packages
 
 * [format](./packages/format)
+* [validation](./packages/validation)
 
 ## Contributing
 
diff --git a/packages/validation/README.md b/packages/validation/README.md
new file mode 100644
index 0000000..af96695
--- /dev/null
+++ b/packages/validation/README.md
@@ -0,0 +1,93 @@
+# @obosbbl/validation
+
+[![NPM Version](https://img.shields.io/npm/v/%40obosbbl%2Fvalidation)](https://www.npmjs.com/package/@obosbbl/validation)
+
+
+A collection of validation methods for both 🇳🇴 and 🇸🇪 with zero dependencies.
+
+## Install
+
+```sh
+# npm
+npm install @obosbbl/validation
+
+# pnpm
+pnpm add @obosbbl/validation
+```
+
+## Usage
+
+The package has two entrypoints, one for `no` and one for `se`. That allows you to import for only the locale you need.
+
+
+```js
+// 🇳🇴 example
+import { validateOrganizationNumber } from '@obosbbl/validation/no';
+validateOrganizationNumber('937052766') // => true
+
+validateOrganizationNumber('000') // => false
+
+// 🇸🇪 example
+import { validateOrganizationNumer } from '@obosbbl/validation/se';
+validateOrganizationNumber('5592221054') // => true
+
+validateOrganizationNumber('000') // => false
+```
+
+## Strictness and formatting characters
+
+The methods are "strict" by default, meaning no formatting characters in the input is allowed.
+This is preferrable, for instance when doing server-side validation, where the input is often expected to be a "clean" value.
+
+If you want to allow formatting characters in the input, you can pass `allowFormatting: true` in the options object to the method.
+Note that this currently allows any formatting characters, not just the just the "expected" ones for the input type.
+
+
+```js
+import { validateOrganizationNumber } from '@obosbbl/validation/no';
+
+validateOrganizationNumber('937052766') // true
+// formatting characters disallowed by default
+validateOrganizationNumber('937 052 766') // false;
+// allow formatting characters
+validateOrganizationNumber('937 052 766', { allowFormatting: true }) // true;
+```
+
+## Methods
+
+* validatePostalCode
+* validatePhoneNumber
+  * supports mobileOnly option
+* validateOrganizationNumber
+  * Check digit verification is currently only implemented for Norwegian organization numbers. For Swedish organiation numbers, we only check the length of the input. PRs are welcome to fix this.
+
+## Example usage with Zod
+
+```js
+import { z } from 'zod';
+import { validatePhoneNumber } from '@obosbbl/validation/no';
+
+const mobileOnlySchema = z.object({
+  name: z.string(),
+  phoneNumber: z
+    .string()
+    .refine(
+      (val) => validatePhoneNumber(val, { mobileOnly: true }),
+      'Telefonnummeret er ikke et gyldig mobilnummer',
+    ),
+});
+
+const validData = {
+  name: 'Kari Nordmann',
+  phoneNumber: '92345678',
+};
+
+mobileOnlySchema.parse(validData); // => { name: 'Kari Nordmann', phoneNumber: '92345678' }
+
+const invalidData = {
+  name: 'Ola Nordmann',
+  phoneNumber: '22865500',
+}
+
+mobileOnlySchema.parse(invalidData); // => throws ZodError
+```
diff --git a/packages/validation/package.json b/packages/validation/package.json
new file mode 100644
index 0000000..4416cd9
--- /dev/null
+++ b/packages/validation/package.json
@@ -0,0 +1,27 @@
+{
+  "name": "@obosbbl/validation",
+  "version": "0.0.0",
+  "description": "A collection of validation methods for OBOS",
+  "repository": {
+    "url": "https://github.com/code-obos/public-frontend-modules"
+  },
+  "license": "MIT",
+  "sideEffects": false,
+  "type": "module",
+  "exports": {
+    "./no": {
+      "types": "./dist/no.d.mts",
+      "default": "./dist/no.mjs"
+    },
+    "./se": {
+      "types": "./dist/se.d.mts",
+      "default": "./dist/se.mjs"
+    }
+  },
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "build": "bunchee"
+  }
+}
diff --git a/packages/validation/src/no.ts b/packages/validation/src/no.ts
new file mode 100644
index 0000000..ccf200c
--- /dev/null
+++ b/packages/validation/src/no.ts
@@ -0,0 +1,86 @@
+import type { ValidatorOptions } from './types';
+import { mod11, stripFormatting } from './utils';
+
+type PostalCodeOptions = ValidatorOptions;
+
+/**
+ * Validates that the input value is a Norwegian postal (zip) code.
+ * @example
+ * ```
+ * validatePostalCode('0000') // => true
+ * ```
+ */
+export function validatePostalCode(
+  value: string,
+  options: PostalCodeOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  return /^\d{4}$/.test(value);
+}
+
+type PhoneNumberOptions = ValidatorOptions & {
+  /**
+   * Whether it should be a mobile number
+   * @default false
+   */
+  mobileOnly?: boolean;
+};
+
+/**
+ * Validates that the input value is a Norwegian phone number.
+ *
+ * Supports mobile only validation.
+ * @example
+ * ```
+ * validatePhoneNumber('00000000') // => true
+ * validatePhoneNumber('90000000', { mobileOnly: true }) // => true
+ * ```
+ */
+export function validatePhoneNumber(
+  value: string,
+  options: PhoneNumberOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  const isPhoneNumber = /^\d{8}$/.test(value);
+
+  if (options.mobileOnly) {
+    // Norwegian mobile phone numbers start with 4 or 9
+    // See https://nkom.no/telefoni-og-telefonnummer/telefonnummer-og-den-norske-nummerplan/alle-nummerserier-for-norske-telefonnumre
+    return isPhoneNumber && ['4', '9'].includes(value.charAt(0));
+  }
+
+  return isPhoneNumber;
+}
+
+type OrganizationNumberOptions = ValidatorOptions;
+
+/**
+ * Validates that the input value is a {@link https://www.brreg.no/om-oss/registrene-vare/om-enhetsregisteret/organisasjonsnummeret/ Norwegian organization number}.
+ * @example
+ * ```
+ * validateOrganizationNumber('000000000') // => true
+ * ```
+ */
+export function validateOrganizationNumber(
+  value: string,
+  options: PhoneNumberOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  /** References:
+   * https://www.brreg.no/om-oss/registrene-vare/om-enhetsregisteret/organisasjonsnummeret/
+   * https://no.wikipedia.org/wiki/Organisasjonsnummer
+   */
+  return mod11(value, [3, 2, 7, 6, 5, 4, 3, 2]);
+}
diff --git a/packages/validation/src/se.ts b/packages/validation/src/se.ts
new file mode 100644
index 0000000..fdf41d0
--- /dev/null
+++ b/packages/validation/src/se.ts
@@ -0,0 +1,85 @@
+import type { ValidatorOptions } from './types';
+import { stripFormatting } from './utils';
+
+type PostalCodeOptions = ValidatorOptions;
+
+/**
+ * Validates that the input value is a Swedish postal (zip) code.
+ * @example
+ * ```
+ * validatePostalCode('00000') // => true
+ * ```
+ */
+export function validatePostalCode(
+  value: string,
+  options: PostalCodeOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  return /^\d{5}$/.test(value);
+}
+
+type PhoneNumberOptions = ValidatorOptions & {
+  /**
+   * Whether it should be a mobile number
+   * @default false
+   */
+  mobileOnly?: boolean;
+};
+
+/**
+ * Validates that the input value is a Swedish phone number.
+ *
+ * Supports mobile only validation.
+ * @example
+ * ```
+ * validatePhoneNumber('00000000') // => true
+ * validatePhoneNumber('000000000') // => true
+ * validatePhoneNumber('0000000000') // => true
+ * validatePhoneNumber('0700000000', { mobileOnly: true }) // => true
+ * ```
+ */
+export function validatePhoneNumber(
+  value: string,
+  options: PhoneNumberOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  if (options.mobileOnly) {
+    // Mobile numbers start with 07, followed by 0/2/3/6/9 and is 10 digits long
+    const isMobileNumber = /^07[02369]\d{7}$/.test(value);
+    return isMobileNumber;
+  }
+
+  const isPhoneNumber = /^0\d{7,9}$/.test(value);
+
+  return isPhoneNumber;
+}
+
+type OrganizationNumberOptions = ValidatorOptions;
+
+/**
+ * Validates that the input value is a {@link https://www.skatteverket.se/foretagochorganisationer/foretagare/startaochregistrera/organisationsnummer.4.361dc8c15312eff6fd235d1.html Swedish organization number}.
+ * @example
+ * ```
+ * validateOrganizationNumber('000000000') // => true
+ * ```
+ */
+export function validateOrganizationNumber(
+  value: string,
+  options: OrganizationNumberOptions = {},
+): boolean {
+  // TODO: Implement checksum validation. For now it only checks the number of digits.
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  return /^\d{10}$/.test(value);
+}
diff --git a/packages/validation/src/types.ts b/packages/validation/src/types.ts
new file mode 100644
index 0000000..19aa395
--- /dev/null
+++ b/packages/validation/src/types.ts
@@ -0,0 +1,7 @@
+export type ValidatorOptions = {
+  /**
+   * Allow formatting characters
+   * @default false
+   */
+  allowFormatting?: boolean;
+};
diff --git a/packages/validation/src/utils.ts b/packages/validation/src/utils.ts
new file mode 100644
index 0000000..a6296f4
--- /dev/null
+++ b/packages/validation/src/utils.ts
@@ -0,0 +1,28 @@
+/** Strip all formatting, leaving only numbers and letters */
+export function stripFormatting(value: string): string {
+  return value.replace(/[^a-zA-Z0-9]/g, '');
+}
+
+/**
+ * Used to validate Norwegian bank account numbers, organization numbers and national identity numbers.
+ * See https://no.wikipedia.org/wiki/MOD11
+ */
+export function mod11(value: string, weights: number[]): boolean {
+  // Since the control digit is a single value, the lengths should be equal
+  if (weights.length + 1 !== value.length) {
+    return false;
+  }
+
+  let sum = 0;
+  weights.forEach((weight, index) => {
+    sum += weight * Number(value[index]);
+  });
+
+  let controlNumber = 11 - (sum % 11);
+
+  if (controlNumber === 11) {
+    controlNumber = 0;
+  }
+
+  return controlNumber === Number(value[value.length - 1]);
+}
diff --git a/packages/validation/src/validation.test.ts b/packages/validation/src/validation.test.ts
new file mode 100644
index 0000000..325512d
--- /dev/null
+++ b/packages/validation/src/validation.test.ts
@@ -0,0 +1,104 @@
+import { describe, expect, test } from 'vitest';
+import * as no from './no';
+import * as se from './se';
+
+describe('no', () => {
+  test.each([
+    ['0179', true],
+    ['01790', false],
+    ['not a number', false],
+  ])('validatePostalCode(%s) -> %s', (input, expected) => {
+    expect(no.validatePostalCode(input)).toBe(expected);
+  });
+
+  test.each([
+    ['22865500', true, undefined],
+    ['90000000', true, undefined],
+    ['40000000', true, undefined],
+    ['22 86 55 00', false, undefined],
+    ['000', false, undefined],
+    ['000000000', false, undefined],
+
+    // formatting
+    ['22 86 55 00', false, { allowFormatting: false }],
+    ['22 86 55 00', true, { allowFormatting: true }],
+
+    // mobile only
+    ['22865500', false, { mobileOnly: true }],
+    ['90000000', true, { mobileOnly: true }],
+    ['40000000', true, { mobileOnly: true }],
+  ])('validatePhoneNumber(%s) -> %s', (input, expected, options) => {
+    expect(no.validatePhoneNumber(input, options)).toBe(expected);
+  });
+
+  test.each([
+    ['937052766', true, undefined],
+    ['937 052 766', false, undefined],
+    ['435256151', false, undefined],
+    ['not a number', false, undefined],
+    ['A37 052 766', false, undefined],
+
+    // formatting
+    ['937 052 766', false, { allowFormatting: false }],
+    ['937 052 766', true, { allowFormatting: true }],
+  ])('validateOrganizationNumber(%s) -> %s', (input, expected, options) => {
+    expect(no.validateOrganizationNumber(input, options)).toBe(expected);
+  });
+});
+
+describe('se', () => {
+  test.each([
+    ['00000', true, undefined],
+    ['000 00', false, undefined],
+    ['not a number', false, undefined],
+
+    // formatting
+    ['000 00', false, { allowFormatting: false }],
+    ['000 00', true, { allowFormatting: true }],
+  ])('validatePostalCode(%s) -> %s', (input, expected, options) => {
+    expect(se.validatePostalCode(input, options)).toBe(expected);
+  });
+
+  test.each([
+    ['08123456', true, undefined],
+    ['0812345', false, undefined],
+    ['031123456', true, undefined],
+    ['030312345678', false, undefined],
+
+    // formatting
+    ['031-123 45', true, { allowFormatting: true }],
+    ['031-123 45', false, { allowFormatting: false }],
+
+    // mobile only
+    // test all valid area codes (070, 072, 073, 076, 079)
+    ['0701234567', true, { mobileOnly: true }],
+    ['0711234567', false, { mobileOnly: true }],
+    ['0721234567', true, { mobileOnly: true }],
+    ['0731234567', true, { mobileOnly: true }],
+    ['0741234567', false, { mobileOnly: true }],
+    ['0751234567', false, { mobileOnly: true }],
+    ['0761234567', true, { mobileOnly: true }],
+    ['0771234567', false, { mobileOnly: true }],
+    ['0781234567', false, { mobileOnly: true }],
+    ['0791234567', true, { mobileOnly: true }],
+    // landline
+    ['031123456', false, { mobileOnly: true }],
+    // too long
+    ['07012345678', false, { mobileOnly: true }],
+  ])('validatePhoneNumber(%s) -> %s', (input, expected, options) => {
+    expect(se.validatePhoneNumber(input, options)).toBe(expected);
+  });
+
+  test.each([
+    ['5592221054', true, undefined],
+    ['559222-1054', false, undefined],
+    ['559222105', false, undefined],
+    ['55922210546', false, undefined],
+
+    // formatting
+    ['559222-1054', false, { allowFormatting: false }],
+    ['559222-1054', true, { allowFormatting: true }],
+  ])('validateOrganizationNumber(%s) -> %s', (input, expected, options) => {
+    expect(se.validateOrganizationNumber(input, options)).toBe(expected);
+  });
+});
diff --git a/packages/validation/tsconfig.json b/packages/validation/tsconfig.json
new file mode 100644
index 0000000..dcbf63f
--- /dev/null
+++ b/packages/validation/tsconfig.json
@@ -0,0 +1,7 @@
+{
+  "extends": "../../tsconfig.json",
+  "include": ["./src/*"],
+  "compilerOptions": {
+    "outDir": "dist"
+  }
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 08bd49c..fa9b314 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -29,6 +29,8 @@ importers:
 
   packages/format: {}
 
+  packages/validation: {}
+
 packages:
 
   '@andrewbranch/untar.js@1.0.3':