The p-rho-T behavior of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) was measured from T = (232 to 400) K with pressures up to 10 MPa using a two-sinker densimeter. The measurements extend from low-density vapor to compressed-liquid states, and include the extended critical region. Vapor pressures from T = (250 to 366) K were also measured. The expanded (k = 2) uncertainty in density is (56.10(-6). rho + 0.0014 kg.m(-3)) at near-ambient conditions, increasing to (99.10(-6). rho + 0.0014 kg.m(-3)) at T = 400 K and p = 10 MPa. The maximum uncertainties in temperature and pressure are 0.004 K and (51.10(-6). p + 2.0 kPa), respectively. The analysis for density accounts for the force transmission error in the magnetic suspension coupling of the densimeter and includes corrections for vertical density gradients in the measuring cell. These data, together with other data from the literature, have been used to develop an equation of state explicit in the Helmholtz energy covering the fluid region from T = (220 to 410) K with pressures up to 30 MPa. Comparisons to experimental data, including other literature data, are given to establish the accuracy of the equation of state.