Software Process Improvement (SPI) has become an active research field, given the evidences that the quality of software processes can significantly influence the final product quality. Therefore, SPI models and guides have been disclosed. Still, there is a lack of studies establishing strategies on how to implement SPI models' best practices. Meanwhile, distributed software development (DSD) is becoming widespread, increasing the complexity and importance of software processes and demanding distributed SPI strategies. This study aims to investigate strategies and mechanisms to promote a distributed and collaborative SPI. ColabSPI, a collaborative and distributed approach to SPI is proposed to supporting process evolution, handling process improvement proposals, and promoting the developers' participation in SPI and communication. Accordingly, during the investigation possible influences to SPI programs were explored and the relationship between them has been mapped, both from the literature and from a field study. SPI was investigated in two contexts: (i) a large organization, counting on distributed development units; and (ii) the FLOSS development environment. Contributions to SPI in the FLOSS development environment took place in the international project Qualipso resulting on a ColabSPI customization to evolve the Qualipso Open Source Maturity Model (OMM) and in the co-authoring of the model. In industrial environment, experimental studies were conducted to validate ColabSPI, revealing that some of the software development practices, including DSD and FLOSS practices, can be successfully applied to SPI and yield a more efficient and effective improvement of the software development process. ColabSPI features are also being considered to the definition of a SPI environment to the Demoiselle process, an open process for software development.