Willdan Group (Willdan) is a company selling professional technical and consulting services to public agencies at all levels of government, public and private utilities, and commercial and industrial firms. The company operates offices in more than a dozen states, with its key operations in California and New York.

The primary markets Willdan serves are: energy engineering; infrastructure and transportation; municipal engineering, planning, and staff augmentation; economic and financial analysis; and national preparedness, through four service segments — Willdan Engineering, Willdan Energy Solutions, Willdan Financial Services and Willdan Homeland Solutions.

In 1964, the company was built by William Stookey and Dan Heil in southern California on a then-unique model of providing outsourced engineering services exclusively to municipalities, especially newly urbanizing cities.

Over the next 50 years, the company's expansion has reflected the increasingly complex challenges facing communities, with a forward-looking focus on energy efficiency, energy engineering, cogeneration, energy savings performance contract, Community Choice Aggregation, smart city and microgrid consulting.

In 2006, Willdan Group, Inc. completed its initial public offerings in NASDAQ, becoming a publicly traded company under the symbol WLDN.

In 2008, Willdan acquired Intergy Corporation, then renamed Willdan Energy Solutions, offering energy efficiency utility program management.

In 2015, Willdan acquired 360 Energy Engineers and Abacus Resource Management, expanding its capabilities into Energy Service Company and Energy Savings Performance Contract services.

Willdan acquired NYC-based Genesys Engineering, P.C., in 2016, bringing Power Engineering services into its portfolio, with an eye to evolution of U.S. power systems toward Distributed generation and microgrids.

Community solar farm development and subscriber management services were launched in 2017 under the Wattcommons platform.

The data analysis firm Integral Analytics, Inc. (IA) was acquired by Willdan in July 2017. IA's software solutions help investor-owned utility and smart city managers solve problems arising from the transformation of an electrical grid facing growth in distributed generation sources, such as solar power and the electric vehicle, effectively harnessing the power of renewable energy and energy storage.