This paper analyzes how professional values and practices influence the character of nonprofit organizations, with data from a random sample of 501(c)(3) operating charities in the San Francisco Bay Area collected between 2003 and 2004. Expended professionalism in the nonprofit world involves not only paid, full-time careers and credentialed expertise but also the integration of professional ideals into the everyday world of charitable work. We develop key indicators of professionalism and measure organizational rationalization as expressed in the use of strategic planning, independent financial audits, quantitative program evaluation, and consultants. As hypothesized, charities operated by paid personnel and full-time management show higher levels of rationalization. While traditional professionals (doctors, lawyers, and the clergy) do not differ significantly from executives with no credentialed background in eschewing business-like practices, managerial professionals champion such efforts actively, as do semi-professionals, albeit more modestly. Management training is also an important spur to rationalization. We assess what is gained and lost and the tension that can arise when nonprofits become professionalized and adopt more methodical, bureaucratic procedures.