Abstract The quality of in situ sea surface temperatures (SSTs) is critical for calibration and validation of satellite SSTs. In situ SSTs come from different countries, agencies, and platforms. As a result, their quality is often suboptimal, nonuniform, and measurement-type specific. This paper describes a system developed at the National Oceanic and Atmospheric Administration (NOAA), the in situ SST Quality Monitor (iQuam; www.star.nesdis.noaa.gov/sod/sst/iquam/). It performs three major functions with the Global Telecommunication System (GTS) data: 1) quality controls (QC) in situ SSTs, using Bayesian reference and buddy checks similar to those adopted in the Met Office, in addition to providing basic screenings, such as duplicate removal, plausibility, platform track, and SST spike checks; 2) monitors quality-controlled SSTs online, in near–real time; and 3) serves reformatted GTS SST data to NOAA and external users with quality flags appended. Currently, iQuam’s web page displays global monthly maps of measurement locations stratified by four in situ platform types (drifters, ships, and tropical and coastal moorings) as well as their corresponding “in situ minus reference” SST statistics. Time series of all corresponding SST and QC statistics are also trended. The web page user can also monitor individual in situ platforms. The current status of iQuam and ongoing improvements are discussed.