diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..bba1044
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,125 @@
+// Copyright (c) Microsoft Corporation and others. Licensed under the MIT license.
+// SPDX-License-Identifier: MIT
+
+/** Represents a parsed SPDX license expression as an Abstract Syntax Tree (AST) */
+export 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 | null
+}
+
+/**
+ * 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
+ */
+export 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
+ */
+export type LicenseRefLookup = (licenseRef: string) => string | null
+
+/** Mode for merging license expressions */
+export type MergeMode = 'OR' | 'AND'
+
+/**
+ * Parses an SPDX expression into an Abstract Syntax Tree (AST) and corrects each node
+ *
+ * @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
+ */
+export function parse(
+  expression: string | SpdxExpression,
+  licenseVisitor?: LicenseVisitor,
+  licenseRefLookup?: LicenseRefLookup
+): SpdxExpression
+
+/**
+ * Converts a parsed expression AST back into an SPDX expression string
+ *
+ * @param obj - An AST representing the parsed expression
+ * @returns The SPDX expression string
+ */
+export function stringify(obj: SpdxExpression): string
+
+/**
+ * Normalizes and returns back a given SPDX expression. Corrects case and formatting inconsistencies.
+ *
+ * @param expression - SPDX expression to normalize
+ * @returns The normalized SPDX expression or null if invalid/empty
+ */
+export function normalize(expression: string | null | undefined): string | null
+
+/**
+ * Normalizes and returns back a single SPDX license identifier
+ *
+ * @param license - Single license identifier to normalize
+ * @returns The normalized SPDX license identifier or null if invalid
+ */
+export function normalizeSingle(license: string | null | undefined): string | null
+
+/**
+ * Checks if the first expression satisfies the second expression
+ *
+ * @param expression1 - First SPDX expression
+ * @param expression2 - Second SPDX expression to check against
+ * @returns True if expression1 satisfies expression2
+ */
+export function satisfies(expression1: string, expression2: string): boolean
+
+/**
+ * Looks up an SPDX identifier by the full license name. Case insensitive matching.
+ *
+ * @param licenseName - Full name of the license
+ * @returns SPDX identifier or null if not found
+ */
+export function lookupByName(licenseName: string | null | undefined): string | null
+
+/**
+ * Merges the proposed expression into the base expression
+ *
+ * @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
+ */
+export function merge(
+  proposed: string | SpdxExpression | null | undefined,
+  base: string | SpdxExpression | null | undefined,
+  mode?: MergeMode
+): string | SpdxExpression | null | undefined
+
+/**
+ * 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
+ *
+ * @param expression - An SPDX license expression in string or object form
+ * @returns The normalized list of license expression leaves equivalent to the input
+ */
+export function expand(expression: string | SpdxExpression): string[][]
+
+/**
+ * Flattens the given expression into an array of all licenses mentioned in the expression
+ *
+ * @param expression - An SPDX license expression in string or object form
+ * @returns An array of all license identifiers in the expression
+ */
+export function flatten(expression: string | SpdxExpression): string[] | undefined
diff --git a/package.json b/package.json
index b9b1089..206d7ea 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"
   ],
diff --git a/tsconfig.json b/tsconfig.json
index a5d3eb9..96e80da 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,5 +5,5 @@
     "checkJs": true,
     "noEmit": true
   },
-  "include": ["index.js"]
+  "include": ["index.js", "index.d.ts"]
 }