Umbilical cord blood unit (CBU) “quantity” continues to grow internationally, while cord blood transplantation (CBT) “quality” remains poorly defined and subject to uncertainty. CBT “quality” is affected by both the product (i.e. CBUs) and CBT processes, with “best practice” varying across countries. To improve overall CBT “quality”, we need to better understand the uncertainty associated with CBUs and CBT processes and how staff manage it. In this qualitative study, we conducted in-depth semi-structured interviews with individuals working in CBT in UK and Japan. We found that understanding of CBT quality by the cord blood community is underpinned by the quality of the CBU, the expertise and collaboration of scientific and clinical stakeholders, trust in collection and testing processes and international accreditation. Importantly, we found that local and individual experience is used to manage uncertainty within CBT, and we propose that selection guidelines should acknowledge the extent of uncertainty in decision-making.