  In this review, the status of measurements of the matter density (Omega), the
vaccuum energy density or cosmological constant (Lambda), the Hubble constant
(H0), and ages of the oldest measured objects (t0) are summarized. Measurements
of the statistics of gravitational lenses and strong gravitational lensing are
discussed in the context of limits on Lambda. Three separate routes to the
Hubble constant are considered: the measurement of time delays in
multiply-imaged quasars, the Sunyaev-Zel'dovich effect in clusters, and
Cepheid-based extragalactic distances. Globular-cluster ages plus a new age
measurement based on radioactive dating of thorium in a metal-poor star are
briefly summarized. Many recent, independent dynamical measurements are
yielding a low value for the matter density (omega ~ 0.2 - 0.3). A wide range
of Hubble constant measurements appear to be converging in the range of 60-80
km/sec/Mpc. Particular attention is paid to sources of systematic error and the
assumptions that underlie many of the measurement methods.
