The success of software component applications dependsupon a number of factors, one of the most important being the quality of components. According to the ISO/IEC 9126 standard, quality characteristics can be used both as goals to be attained in the processes of developing, selecting or acquiring components and as criteria for predicting the properties of final applications. This chapter identifies the quality characteristics and sub-characteristics most relevant for software components and organizes them in dimensions that are critical to their assessment. A quality guide is presented, which was elaborated through a field research carried out with developers of components and component-based applications. A software quality evaluation model was used to treat collected data.