Despite the high fluorophilicity of boron, certain organoboranes and boronate esters can be employed as CsF phase-transfer nucleophilic fluorination catalysts. Chiral induction during fluorination with borane catalysts also can be achieved to some extent, however limited catalyst stability under these reaction conditions precludes realising high e.e. in the systems studied to date. Regarding the factors controlling effective catalysis, as expected, nucleophilic fluorination reactivity is impacted by B-F bond strength, which is dependent on borane Lewis acidity towards fluoride. Sufficient fluoride affinity is required for the borane to react with CsF, however if fluoride affinity is too high the resultant fluoroborate does not effectively transfer fluoride to electrophiles. Furthermore, nucleophilic fluorination is most effective under conditions that preclude good ligation of the cation as strong binding of Cs + weakens the Cs⋯F-B interaction, strengthening the B-F bond and thereby leading to less reactive fluoroborates. In terms of predictability, boranes with calculated fluoride affinity of 100 -120 kJ•mol -1 (vs. Me3Si + ) appear to be suitable candidates as nucleophilic fluorination catalysts, with the caveat that other factors (e.g. borane stability under the reaction conditions / forming the correct fluoroborate aggregation / Cs + ligation level in solution) are also important to consider. When these prerequisites are met, simple boranes are effective catalysts for nucleophilic fluorination using CsF, including to access useful products (e.g. -fluoroamines). Finally, this work highlights that the established dogma that boranes are highly fluorophilic / strong fluoride acceptors, does not always hold.