diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..c5f9755
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,177 @@
+/**
+ * TypeScript type definitions for @clearlydefined/spdx package
+ *
+ * This module provides utilities for parsing, normalizing, and manipulating SPDX license expressions. It supports
+ * operations like parsing expressions into ASTs, converting back to strings, checking license satisfaction, and merging
+ * license expressions.
+ */
+
+declare module '@clearlydefined/spdx' {
+  /** Represents a parsed SPDX license expression as an Abstract Syntax Tree (AST) */
+  interface SpdxExpression {
+    /** The SPDX license identifier (e.g., 'MIT', 'Apache-2.0') */
+    license?: string
+    /** Whether the license allows later versions (indicated by '+' suffix) */
+    plus?: boolean
+    /** License exception identifier (e.g., 'Classpath-exception-2.0') */
+    exception?: string
+    /** Logical conjunction operator ('and' or 'or') */
+    conjunction?: 'and' | 'or'
+    /** Left operand in a binary expression */
+    left?: SpdxExpression
+    /** Right operand in a binary expression */
+    right?: SpdxExpression
+    /** Indicates this is a NOASSERTION expression */
+    noassertion?: boolean
+  }
+
+  /**
+   * Visitor function type for processing license nodes during parsing
+   *
+   * @param license - The license identifier to process
+   * @returns The normalized license identifier or null if invalid
+   */
+  type LicenseVisitor = (license: string) => string | null
+
+  /**
+   * Lookup function type for resolving license references
+   *
+   * @param licenseRef - The license reference to resolve
+   * @returns The resolved license identifier or null if not found
+   */
+  type LicenseRefLookup = (licenseRef: string) => string | null
+
+  /** Mode for merging license expressions */
+  type MergeMode = 'OR' | 'AND'
+
+  /**
+   * Parses an SPDX expression into an Abstract Syntax Tree (AST) and corrects each node
+   *
+   * @example
+   *   ```typescript
+   *   const ast = parse('MIT OR Apache-2.0');
+   *   console.log(ast.conjunction); // 'or'
+   *   ```
+   *
+   * @param expression - SPDX expression string to parse
+   * @param licenseVisitor - Optional visitor function to clean each license node
+   * @param licenseRefLookup - Optional lookup function to resolve license references
+   * @returns The AST representing the parsed expression
+   */
+  function parse(
+    expression: string | SpdxExpression,
+    licenseVisitor?: LicenseVisitor,
+    licenseRefLookup?: LicenseRefLookup
+  ): SpdxExpression
+
+  /**
+   * Converts a parsed expression AST back into an SPDX expression string
+   *
+   * @example
+   *   ```typescript
+   *   const ast = { conjunction: 'or', left: { license: 'MIT' }, right: { license: 'Apache-2.0' } };
+   *   const expression = stringify(ast); // 'MIT OR Apache-2.0'
+   *   ```
+   *
+   * @param obj - An AST representing the parsed expression
+   * @returns The SPDX expression string
+   */
+  function stringify(obj: SpdxExpression): string
+
+  /**
+   * Normalizes and returns back a given SPDX expression Corrects case and formatting inconsistencies
+   *
+   * @example
+   *   ```typescript
+   *   const normalized = normalize('mit OR apache-2.0'); // 'MIT OR Apache-2.0'
+   *   ```
+   *
+   * @param expression - SPDX expression to normalize
+   * @returns The normalized SPDX expression or null if invalid/empty
+   */
+  function normalize(expression: string): string | null
+
+  /**
+   * Normalizes and returns back a single SPDX license identifier
+   *
+   * @example
+   *   ```typescript
+   *   const normalized = normalizeSingle('mit'); // 'MIT'
+   *   ```
+   *
+   * @param license - Single license identifier to normalize
+   * @returns The normalized SPDX license identifier or null if invalid
+   */
+  function normalizeSingle(license: string): string | null
+
+  /**
+   * Checks if the first expression satisfies the second expression
+   *
+   * @example
+   *   ```typescript
+   *   const satisfied = satisfies('MIT', 'MIT OR Apache-2.0'); // true
+   *   ```
+   *
+   * @param expression1 - First SPDX expression
+   * @param expression2 - Second SPDX expression to check against
+   * @returns True if expression1 satisfies expression2
+   */
+  function satisfies(expression1: string, expression2: string): boolean
+
+  /**
+   * Looks up an SPDX identifier by the full license name Case insensitive matching
+   *
+   * @example
+   *   ```typescript
+   *   const spdxId = lookupByName('Common Public License 1.0'); // 'CPL-1.0'
+   *   ```
+   *
+   * @param licenseName - Full name of the license
+   * @returns SPDX identifier or null if not found
+   */
+  function lookupByName(licenseName: string): string | null
+
+  /**
+   * Merges the proposed expression into the base expression
+   *
+   * @example
+   *   ```typescript
+   *   const merged = merge('GPL-3.0', 'MIT OR Apache-2.0', 'OR'); // 'MIT OR Apache-2.0 OR GPL-3.0'
+   *   ```
+   *
+   * @param proposed - The proposed license expression to merge
+   * @param base - The base license expression to merge into
+   * @param mode - Merge mode, either 'OR' (default) or 'AND'
+   * @returns The merged license expression
+   */
+  function merge(proposed: string | SpdxExpression, base: string | SpdxExpression, mode?: MergeMode): string
+
+  /**
+   * Expands the given expression into an equivalent array where each member is an array of licenses AND'd together and
+   * the members are OR'd together
+   *
+   * @example
+   *   ```typescript
+   *   const expanded = expand('(MIT OR ISC) AND GPL-3.0');
+   *   // Returns: [['GPL-3.0', 'MIT'], ['GPL-3.0', 'ISC']]
+   *   ```
+   *
+   * @param expression - An SPDX license expression in string or object form
+   * @returns The normalized list of license expression leaves equivalent to the input
+   */
+  function expand(expression: string | SpdxExpression): string[][]
+
+  /**
+   * Flattens the given expression into an array of all licenses mentioned in the expression
+   *
+   * @example
+   *   ```typescript
+   *   const flattened = flatten('MIT OR (Apache-2.0 AND GPL-3.0)');
+   *   // Returns: ['Apache-2.0', 'GPL-3.0', 'MIT']
+   *   ```
+   *
+   * @param expression - An SPDX license expression in string or object form
+   * @returns An array of all license identifiers in the expression
+   */
+  function flatten(expression: string | SpdxExpression): string[]
+}
diff --git a/package.json b/package.json
index 2026ef2..3e0f29e 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "url": "git+https://github.com/clearlydefined/spdx.git"
   },
   "main": "index.js",
+  "types": "index.d.ts",
   "keywords": [
     "spdx"
   ],