Films at the air/water interface and Langmuir-Blodgett films of docosylamine have been formed over subphases having a wide range of pH values and containing a variety of different additives. These include polyacrylic acid, valeric acid, potassium arsenate, sodium arsenate, and chloroplatinic acid. Some of these systems have received some previous study but earlier workers have not all made use of X-ray diffraction to confirm the existence of a regular layer structure or to find the repeat distance associated with these layers. We agree with the conclusion arrived at by Gaines, namely that, in the case of films formed over subphases containing NaOH and valeric acid, carbon dioxide in the atmosphere combines with the amine to form a carbamate. These films are Y-type. The films formed over a subphase containing sodium arsenate incorporate the arsenate group and are also Y-type. On the other hand films formed over potassium arsenate are of inferior quality showing that the cation does more than simply act as a counterion in solution. Films formed over a subphase containing chloroplatinic acid exhibit a layer structure but are of poor quality and are Y-type.