The 2014 NCCN Clinical Practice Guidelines in Oncology for Chronic Myelogenous Leukemia recommend quantitative reverse-transcription polymerase chain reaction (qRT-PCR) standardized to International Scale (IS) as the preferred method for monitoring molecular response to tyrosine kinase inhibitor (TKI) therapy. A BCR-ABL1 transcript level of 10% or less (IS) is now included as the response milestone at 3 and 6 months. Change of therapy to an alternate TKI is recommended for patients with BCR-ABL1 transcript levels greater than 10% (IS) at 3 months after primary treatment with imatinib. Continuing the same dose of TKI or switching to an alternate TKI are options for patients with BCR-ABL1 transcript levels greater than 10% (IS) at 3 months after primary treatment with dasatinib or nilotinib. The guidelines recommend 6-month evaluation with qRT-PCR (IS) for patients with BCR-ABL1 transcript levels greater than 10% at 3 months. Monitoring with qRT-PCR (IS) every 3 months is recommended for all patients, including those who meet response milestones at 3, 6, 12, and 18 months (BCR-ABL1 transcript level ≤10% [IS] at 3 and 6 months, complete cytogenetic response at 12 and 18 months).