This book addresses an often neglected aspect of econometrics, the question of how to assess the specification, strengths, weaknesses, limits, and sensitive features of a model. The contributions are the result of a five-year inter-university research project to improve understanding of concepts of model reliability.Contents: Introduction, David A. Belsley and Edwin Kuh. Wholesale and Retail Prices: Bivariate Time Series Modeling with Forecastable Error Variables, C.W.J. Granger, R.P. Robins, and Robert F. Engle.