The Clinical Laboratory Improvement Amendments (CLIA) set standards designed to improve the quality of all laboratory testing. In the first portion of this chapter, we discuss the CLIA requirements that apply to most Immunohistochemistry laboratories, and explain topics such as certification, test complexity, patient test management, proficiency testing, personnel, quality control, quality assurance, and compliance. The second portion of this chapter addresses the most common problems encountered in immunohistochemical procedures and the appropriate solutions to correct them.