The pure rotational spectra of 13 isotopically substituted forms of vinyl cyanide, H2C=CHCN, have been measured in the microwave and millimeter-wave frequency regions. Spectra of all monosubstituted species containing13C,15N, and D have been observed, as well as those of all13C-monosubstituted species of H2C=CDCN, of bothcis- andtrans-isotopomers of HDC=CHCN and HDC=CDCN, and of D2C=CDCN. Various methods have been used to evaluate the molecular geometry.14N quadrupole hyperfine structure has been resolved for four isotopomers, using a cavity pulsed Fourier transform microwave spectrometer. The variation of the constants with isotopomer has been used to evaluate the principal values of the quadrupole tensor. The CN bond is confirmed to be essentially cylindrically symmetrical.