The X‐ray structures at 120 K of C6H5SeO2N(CH3)2 (1) and C6H5SeO2NHCH3 (2) were determined from single crystal data, the structure of C6H5SeO2NH2 (3) was determined from a twin. The structure of (1) is composed of isolated molecules, that of (2) of dimers via H‐bonds and the structure of (3) forms infinite chains. The SeN lengths are 1.815(2) Å for (1), 1.791(2) Å for (2), and 1.781(6) Å for (3).