The W40 complex is a nearby site of intermediate-mass star formation associated with a cold molecular cloud (~10⁴ M_⊙) and includes a blistered H II region powered by an OB association and two interconnected cavities, forming an hour-glass shape on large scales. The main cluster is located just northwest of the narrow waist where the two cavities are joined. The bright-rimmed clouds at the cavity walls show clearly that dense clumps and pillars are illuminated from inside by the cluster. The OB association is comprised of IRS/OS1a (O9.5), IRS/OS2b (B4) and IRS/OS3a (B3) and an associated stellar cluster of pre-main-sequence (PMS) stars.