The U.S. GEOTRACES Pacific Meridional Transect (GP15) special issue is a collection of articles focusing on the 2018 GP15 cruise, which sampled along 152°W from Alaska to Tahiti. As the first meridional cruise of the U.S. GEOTRACES program, it aligns with the CLIVAR P16 line. The sampled trace elements and isotopes (TEIs), including micronutrients, are crucial for understanding various oceanic processes, such as those occurring in ocean margins, subarctic high-nutrient low-chlorophyll (HNLC) waters, deep water, hydrothermal plumes, oxygen minimum zones, equatorial upwelling, and the oligotrophic waters of the South Pacific gyre.