The properties of infinite nuclear matter are studied in the model relativistic quantum field theory of Walecka. Neutral scalar and vector meson exchange reproduces the basic Lorentz structure of the observed nucleon‐nucleon interaction, and the consequences of this structure are studied in detail. In the mean‐field approximation, nuclear saturation involves a cancellation between large attractive and repulsive components in the average potential energy. The attractive scalar field decreases the nucleon mass significantly, and the strong vector repulsion implies a stiff high‐density equation of state. Corrections to the mean‐field approach arising from vacuum fluctuations, self‐consistent nucleon exchange, and two‐nucleon correlations are examined. These have a small effect on the condensed meson fields but may produce significant changes in the binding energy. Corrections to the mean‐field equation of state are small at high density.