Introduction. Part I. Meteorology in 1900. An Empirical Tradition: Climatology. A Theoretical Tradition: Physics of the Atmosphere. A Practical Tradition: Weather Forecasting. Part II. Meteorology in the First Half ofthe 20th Century. Vilhelm Bjerkness Program to Unify Meteorology. Lewis Fry Richardson: The First Person to Compute the Weather. The Growth of Meteorology. Meteorological Calculation in the Interwar Period. The Effect of World War II on Meteorology. Part III. The Beginning of the Computer Era in Meteorology. John von Neumanns Meteorology Project. The Acceptance of Numerical Meteorology. The Unification of Meteorology. The Recognition of Limits to Weather Prediction. Endnotes. Notes on Sources. References. Index.