There are various ways to classify types and motivations for M&A activities, but they are commonly divided into four main categories: vertical M&A, horizontal M&A, conglomerate M&A, and cross-border M&A.

Vertical M&A occurs between two companies in the same industry but at different stages of production. Horizontal M&A happens between two companies in the same industry and at the same stage of production. Conglomerate M&A involves two companies from different industries. Cross-border M&A takes place between two companies headquartered in different countries. Since M&A transactions occur across various industries and scales worldwide, their motivations are explained through multiple theories, the most common being synergy theory, agency theory, market power theory, and diversification theory.