This is a phase 3, multi-center, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of CTAP101 Capsules administered for 26 weeks to treat SHPT in subjects ≥18 years of age with stage 3 or 4 CKD and vitamin D insufficiency. The study will be conducted at approximately 40 sites within the United States (US). Approximately 550 subjects will be screened to randomize approximately 210 eligible subjects, stratified by CKD stage (approximately 105 subjects in each stage) in a 2:1 ratio to receive either CTAP101 Capsules or matching placebo. An Interactive Voice Response System (IVRS) will provide study treatment group assignments using the computer-generated randomization code provided by the IVRS vendor. Subjects will receive an initial daily dose of 1 capsule (CTAP101 Capsules, 30 µg, or matching placebo) for the first 12 weeks. After l2 weeks (visit 8) and per pre-defined criteria, the dose may be increased in a blinded fashion by the IVRS with oversight by an independent medical monitor.