R/V METEOR Cruise M54 comprised three legs focusing on the Costa Rican - Nicaraguan segment of the Middle America Trench. While Leg 1 concentrated on the seismic imaging of vent structures and sub-surface fluid pathways, Leg 2 and Leg 3 carried out geochemical and sedimentological investigation toward the objectives of SFB 574 - Volatiles and Fluids in Subduction Zones. These measurements were supplemented by heat flow surveys and the recovery and re-deployment of an offshore seismic network. More specifically, the following objectives were pursued during the individual Cruise Legs: M54/1 was devoted to high-resolution seismic profiling in order to obtain the geometry and thickness of the incoming sediment packages. Special attention was given to the distribution of gas hydrates as evident in the BSR (Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover), which is linked to upward fluid flow. In combination of different geophysical methods, applied to small-scale selected areas, the quantification of physical properties of the sediments and their pore fluids was attempted. During M54/2, sediment coring and heat flux measurements along pre-selected profiles were used, on one hand, to investigate early diagenetic processes, determine the sediment physical properties, and collect volcanic ash layers for the reconstruction of the history of explosive volcanisms. On the other hand, a special focus was put on the thermal structure of the lithospheric plate and thus the constraining of the seismogenic zone. Additionally, the thermal anomalies at and around fluid conduits and slump features were measured. M54/3 attempted the identification and sampling of sites influenced by venting of methane-rich fluids in order to assess the dewatering history of the area, to quantify the amount of fluids and dissolved gases released from the seafloor, and the turnover of methane in the sediment as well as in the water column, finally to ascertain source depth and residence time of fluids. At the same time, a seismic network installed in April 2002 during R/V SONNE cruise SO163-2 was recovered and redeployed for a further year. A benthic lander deployed at Jaco Scarp was also retrieved.