The paper describes an ongoing project to define a suitable process model for software process improvement in small to medium organizations. This is being carried out as a collaborative project between Leeds Metropolitan University and four small to medium companies who are currently implementing SPI programs. Key features of the PRISMS process are: explicitly relating improvement goals to business goals, which are used to choose and prioritize key process areas for improvement; the use of a simplified and tailorable assessment method based on CMM [1]; the definition and use of metrics from the outset; and mechanisms to encourage maximum transparency in the process and participation by all stakeholders.