Background: Improved health outcomes for critically ill infants including neurodevelopmental, immunological, and cost benefits are dependent upon the dose and duration of mother's own milk feedings. However, mothers of infants admitted to the neonatal intensive care unit (NICU) must express their milk (pump-dependent) and often struggle with milk production. Purpose: To examine the state of the science on nonpharmacologic modifiable expression factors that may influence milk production in pump-dependent mothers of critically ill infants admitted to the NICU. Data Sources: PubMed, Embase, and CINAHL databases from 2005 to 2020. Search Strategy: Guided by the lactation conceptual model, the authors searched for peer-reviewed studies with terms related to milk volume, pump dependency, critically ill infants, and modifiable factors, which may influence milk volume and assessed 46 eligible studies. Data Extraction: Data were extracted by 3 reviewers with a systematic staged review approach. Results: Evidence from 26 articles found expressed milk volume may be influenced by multiple potentially modifiable factors. Simultaneous expression with a hospital-grade electric pump at least 5 times per day beginning 3 to 6 hours after delivery, and adding complementary techniques including hand expression, hands-on-pumping, music, breast massage, warm compresses, skin-to-skin care, and the mother expressing near her infant may promote increased milk volume. Implications for Practice and Research: Healthcare providers should assist pump-dependent mothers with early initiation and frequent milk removal with a hospital-grade breast pump. Further research is needed to explore optimal frequency of expressions, dose and timing of skin-to-skin care, and other targeted strategies to improve expressed milk volume.