Software Development managers recognize that project team dynamics is a key component of the success of any project. Managers can have a project with well-defined goals, an adequate schedule, technically skilled people and all the necessary tools, but if the project team members cannot communicate and collaborate effectively with each other and with end users, then project success is at risk. Common problems with non-technical skills include dysfunctional communication, negative attitudes, uncooperativeness, mistrust, avoidance, and ineffective negotiations between team members and users. Such problems must be identified and addressed to improve individual and team performance. There are tools available that assist in measuring the effectiveness of the technical skills and processes that teams use to execute projects, but there are no proven tools to effectively measure the non-technical skills of software developers. Other industries (e.g. airline and medical) are also finding that teamwork issues are related to non-technical skills, as well as lack of technical expertise. These industries are beginning to use behavioral marker systems to structure individual and team assessments. Behavioral markers are observable behaviors that impact individual or team performance. This dissertation work explores and develops a behavioral marker system tool, adapted from model in other industries, to assist managers in assessing the non-technical skills of project team individuals within groups. An empirical study was also conducted to prove the validity of the tool and the report is included in this study. We also developed and report upon empirical work that assesses how Social Sensitivity (a non-technical skill) impacts team performance. There are four components to this work: Develop a useful non-technical skills taxonomy; Develop a behavioral marker system for software developers and the non-technical skills taxonomy; Validate the software developer behavioral marker system; Investigate specifically the effect of social sensitivity on team performance. The evaluation is based on data collected from experiments. The overall goal of this work is to provide software development team managers with a methodology to evaluate and provide feedback on the non-technical skills of software developers and to investigate if a particular non-technical skill can positively affect team performance.