The Contribution Taxonomy Project will develop a taxonomy of the contributions made by Wikimedia communities, measure the contributions in that taxonomy, and elicit trends in volunteer contributions to the projects. By creating a comprehensive classification of the different types of roles volunteers may take, and by using our data to find active contributors that fill these roles, the project is intended to bring to light the historical and continuing development of Wikimedia wikis. The project will also hopefully bring attention to previously unrecognized contributors in key areas.
To date, most research inside and outside the movement has focused on edit count as the key measurement of activity levels. A few other sources, such as stats.wikimedia.org, also include some measurements of article growth and number of files, but few studies dig deeper.
Volunteers with high edit counts are easily discoverable through a variety of avenues, especially through each project's list of contributors by edit count (Example: User:Emijrp/List of Wikimedians by number of edits). The age and retention of editors, both new and old has been looked at closely by the Editor Trends Study at the Foundation, though that study intentionally did not address the type or value of edits made. Edit count is one important measurement of how active a Wikimedian is. However, it is a metric of community involvement that can highlight some volunteer efforts while masking others in the diverse spectrum of roles within a project. As researchers from Cornell put in it in their paper on finding social roles on Wikipedia:
Though formal roles are few, Wikipedians recognize a number of informal roles as well, including fighting vandalism, welcoming new users, managing the featured article process (Viegas 2007) and writing tools to help the community (Cosley et al. 2007). [...] Studying these informal roles will help us understand how the coordination problem of collective action can be addressed through community processes and monitoring, possibly giving insight into the future health of the community... 
By putting some numbers to the different kinds of activities that make Wikimedia wikis function as they do, we will be able to understand the composition of our communities and make better informed decisions aimed at meeting our strategic goals.
The idea for this project was generated during a visit by several volunteers to the Foundation. In collaboration with the Community Department, Damian Finol and Steven Walling developed a draft taxonomy of contributions and will produce some initial surveys of the largest projects. The project is currently one of a set undertaken by Walling's fellowship in the Community Department.
The following is a draft taxonomy of contributions, and is open to revision. It mostly functions as a mind map of ideas for activities that we want to measure in the project. Currently, it pertains to Wikipedia and contributions outside any specific project. At this point the taxonomy is as general as possible, and may cover roles not seen in some languages or take a broader view of a task than some communities might exhibit in practice. Keep in mind that this is not a hierarchical categorization, but rather possible areas of activity for contributors to spend a good deal of their time on.