Despite common wisdom that suggests otherwise, Agile development practices and CMMI are compatible. Research into Software Engineering and studies of Extreme Programming (XP), from which many of the practices of i-Proving are based, have concluded that XP practices are complementary to the goals of the CMM. To quote Mark C. Paulk of the SEI:
For those interested in process improvement, the ideas in XP should be carefully considered for adoption where appropriate in an organization’s business environment since XP can be used to address many of the CMM Level 2 and 3 practices.
The original article is available here: Extreme Programming from a CMMI Perspective
Other studies involving the Scrum methodology have also concluded that the Agile practices promoted by Scrum and CMMI are not only compatible but an organization already operating at a high level of CMMI compliance can realize even greater gains in productivity by introducing Scrum.