In global economy software development has to adapt to changing customer demands very quickly. In some cases projects are too big for one company to handle or involve using several fundamentally different technologies. Strategic partnerships between software companies are a widely accepted solution in those situations. When dealing with software development teams spanning across several companies project managers have to solve many co-operation and coordination issues. The co-operation issues in such projects are often closely similar to those described in papers on Global Software Development. The purpose of this thesis is to analyze some of the related studies on Global Software Development and formulate main issues of multi-company software development. Additionally, this thesis analyses papers on company co-operation and customer relations. The scope of this thesis is limited to projects in which participating companies are equal partners. The research is further limited by selecting a few problem areas for analysis: managing resources, reporting, coordinating between teams, managing customer relations and team inter-dependency. Multi-company development issues are gathered by analyzing the available materials on multi-site development, inter-company co-operation and customer relation management. The resulting data is then compared to empirical observations in the case study chapter. Since the research area is limited and the materials on the topic are not covering all possible multicompany development issues, some future research directions are outlined in the discussion chapter.