This paper describes an efficient analytical/ numerical method that determines the responses of multiple floating structures in waves in the vicinity of each other. The analysis considers the interaction of multiple structures including their scattering and radiation in waves. Multiple structure interaction in waves by the well-known direct method of linear diffraction/radiation is in principle possible with moderate modification of the single-structure diffraction/radiation problem. However, the direct method, while quite accurate and efficient in solving hydrodynamic problems, demands a large amount of memory and requires considerable execution time. It is recognized that for a large number of modules in a structure this approach has serious limitation due to limited personal computer storage and prohibitively excessive execution time. Moreover, the accuracy of this solution for a large multi-moduled structure, if possible, may not be acceptable. The efficiency of the present analysis is accomplished by marrying the direct method of linear diffraction/radiation for arbitrary structure geometry with a semi-closed analytical method of multiple scattering developed for an array composed of vertical cylindrical structures. The analysis is applied to structures of arbitrary geometry. Moreover, the dynamic response of the structure is also included in the analysis. The Mobile Offshore Base (MOB) proposed for use by the US Navy is an interconnected multi-moduled floating offshore structure. The present method will provide the responses, e.g., the six degrees of motion of the individual modules of the MOB and the corresponding connector loads, when subjected to regular waves incident at any heading. The capabilities, and accuracy of the method are demonstrated and its speed relative to the conventional direct method is discussed. Several numerical examples of the multiple interaction method are given. Comparisons are made with the conventional diffraction/radiation results wherever feasible as well as with the available experimental data.