Abstract: A process for the preparation of ammonium nitrate by the reaction of nitric acid with ammonia in two stages at elevated temperature, in which the first stage is carried out at elevated pressure and the second stage is carried out at atmospheric pressure. The heat of neutralization released in the first stage is used to vaporize a portion of the reactor contents, the remaining heat of reaction being utilized to produce steam. The vapor leaving the first stage develops a pressure which controls the valve regulating the amount of heat recovered by steam generation. The valve is opened when the pressure of the vapor exceeds a set value, usually in the range of 3.4 to 4.8 bars. Decomposition products of ammonium nitrate are also measured and override the pressure regulated control of the proporiton of heat recovered by steam generation, so as to maintain ammonium nitrate decomposition within acceptable limits. An apparatus for carrying out the process is also disclosed.