The ACCOBAMS Survey Initiative (ASI) is a pilot program aimed at establishing an integrated and coordinated monitoring system for cetaceans in the Mediterranean Sea and contiguous Atlantic area. Conducted in collaboration with Mediterranean coastal countries, the ASI supports European and regional policies, particularly the EU Marine Strategy Framework Directive and the Ecosystem Approach process. In summer 2018, a synoptic survey was conducted using aircraft and vessels to estimate species density and abundance through a line-transect sampling framework. The survey covered 77% of the Mediterranean Sea and the Gulf of Cádiz, monitoring over 55,000 km along predetermined transects. Nine cetacean species were encountered, with striped dolphins being the most abundant (N=426,744), followed by common dolphins (N=65,359), bottlenose dolphins (N=63,333), and Risso’s dolphins (N=26,006). Cuvier’s beaked whales (N=2,929) and long-finned pilot whales (N=5,540) were also observed. Fin whales were corrected for availability and perception biases, resulting in an estimated abundance of 3,282 individuals. The ASI provides a baseline for future systematic monitoring programs and contributes to conservation and management decisions. The survey highlights the need for comprehensive integration of design- and model-based estimates and spatial modeling to better understand cetacean distribution and abundance in the region.The ACCOBAMS Survey Initiative (ASI) is a pilot program aimed at establishing an integrated and coordinated monitoring system for cetaceans in the Mediterranean Sea and contiguous Atlantic area. Conducted in collaboration with Mediterranean coastal countries, the ASI supports European and regional policies, particularly the EU Marine Strategy Framework Directive and the Ecosystem Approach process. In summer 2018, a synoptic survey was conducted using aircraft and vessels to estimate species density and abundance through a line-transect sampling framework. The survey covered 77% of the Mediterranean Sea and the Gulf of Cádiz, monitoring over 55,000 km along predetermined transects. Nine cetacean species were encountered, with striped dolphins being the most abundant (N=426,744), followed by common dolphins (N=65,359), bottlenose dolphins (N=63,333), and Risso’s dolphins (N=26,006). Cuvier’s beaked whales (N=2,929) and long-finned pilot whales (N=5,540) were also observed. Fin whales were corrected for availability and perception biases, resulting in an estimated abundance of 3,282 individuals. The ASI provides a baseline for future systematic monitoring programs and contributes to conservation and management decisions. The survey highlights the need for comprehensive integration of design- and model-based estimates and spatial modeling to better understand cetacean distribution and abundance in the region.