Software Process Improvement (SPI) has been widely adopted by software organizations to enhance their capability to effectively deliver quality software. The approach has several positive merits. But many initiatives fail because the software processes are never adopted in practice. This paper offers a comparative analysis of the implementation strategies and outcomes of 18 SPI initiatives within Ericsson. The analysis draws upon concepts from the diffusion of innovations literature and leads to four different process implementation strategies – High Way, Country Road, Crossroads, and Dead End Street. These roads to software process implementation target different levels of practice and they rely on different mixtures of process push and practice pull. Our research suggests that the High Way with its combination of strong push and strong pull is the most promising road to implementation success, whereas the other roads imply serious barriers to success.