High pressure is a defining feature of marine sediments and a major factor influencing biogeochemical processes, the deep biosphere, and gas-hydrate deposits. However, the considerable technical challenges of recovering, handling, and analyzing sediment cores under pressure limit the detailed investigation of the impact of pressure on marine sediment processes. Here we describe recent developments in high-pressure coring, handling, and analysis. In particular, we provide an update on a further development of the European hydrate autoclave coring equipment (HYACE) coring system during the recent Development of the HYACE Tools in New Tests on Hydrates (HYACINTH) project. The two high-pressure coring systems (HYACE rotary corer and Fugro percussion corer) have now successfully recovered good quality cores, under high pressure (maximum 25 MPa), from a range of ocean sediments. Gas hydrates within these have been well preserved, and a high-pressure core transfer, logging, and subsampling system has been successfully developed and used. This includes the pressurized core subsampling and extrusion system (PRESS, maximum 25 MPa), which removes any potential contamination on the outer core by producing a central subcore; this subcore can then be sliced and transferred to high-pressure vessels for biogeochemical experiments and microbial enrichment and isolation using the DeepIsoBUG system (maximum 100 MPa). These systems have already contributed to both gas-hydrate and deep-biosphere research by demonstrating the presence of free methane gas in sediments in the gas-hydrate stability zone and the formation of maximum microbial cell densities at elevated pressures (up to 80 MPa) during bacterial enrichment experiments.