In 1972, D.R. Cox proposed the semiparametric model
for the hazard at time
t
for an individual with covariates
z
. Here, the hazard is the instantaneous conditional probability of failure at
t
given that failure has not happened before
t
.
The Cox model has had enormous influence in the theory and practice of biostatistics, and this article surveys its definition, history, basic use, estimators and algorithms, asymptotic properties, use of time‐dependent covariates, model checking, and alternatives and extensions.