While we have learned a great deal from Software Process Improvement (SPI) research to date, no earlier study has been designed from the outset to examine the relationship between SPI and business success in software development small- to- medium- sized companies (software SMEs). Since business processes are generally acknowledged as having an important role to play in supporting business success, it follows that the software development process (a large and complex component of the overall business process) has an important contribution to make in supporting business success in software development companies. However, to date we have very little evidence regarding the role of SPI in supporting business success, especially for software SMEs. The need for SPI is dependent on the extent of situational change in a software development setting, and therefore any examination of the relationship between SPI and business success would be deficient if it did not also examine the extent of situational change. Therefore, this thesis describes a novel approach to examining SPI, situational change and business success in software development companies. Furthermore, having discharged this new approach to 15 software SMEs, this thesis makes the important new discovery that the amount of SPI implemented in a software SME is positively associated with the extent of business success – especially when the degree of situational change is taken into account. This thesis describes the first published study to examine the relationship between SPI, situational change and business success in software SMEs. The findings suggest that there are business benefits to implementing SPI in software SMEs, with the degree of situational change being an important factor informing SPI initiatives. Furthermore, this research has yielded valuable new insights into the nature of SPI, situational change and business success in software SMEs.