This paper treats the theory of identification presented in Haavelmo's
classic work, The Probability Approach in Econometrics. This was the
first identification theory for stochastic models to be developed in e
conometrics. The paper presents a detailed commentary on Haavelmo's an
alysis. It also examines the development of Haavelmo's theory from Fri
sch's analysis of multicollinearity and also the relationship between
Haavelmo's analysis and later work on identification.