Professional open source is an open-source software business model where an open-source software vendor generates revenue from paid professional services, maintenance and support provided along with the software. Some open-source software vendors also provide commercial licenses of open-source software or customized versions of open-source software to specific customers .
As open-source software began to become popular in the 1990s with the introduction of Linux, business hesitated to adopt it because of fears that no single entity guaranteed its stability or support. As a consequence, larger businesses would often choose commercially distributed software over a product that was released under an open-source license. However, there has been much growth in the number of professional open-source companies – made popular by companies like Liferay, Inc., OpenSearchServer, Red Hat, MySQL AB, and JBoss. The business model of these companies tries "to offer open-source software with a free license, while using professional services, maintenance and support for these products to derive revenue."