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Well-defined uniaxial micro-tensile tests are performed on single-crystal ferrite specimens with three different orientations. All specimens reveal a highly reproducible plastic behavior. The {110}<111> and {112}<111> slip systems equally contribute to the deformation, while all other (complex) slip traces can be identified as cross-slip and ‘pencil glide’. No {123}<111> slip system traces were observed. The critical resolved shear stresses of the two active slip systems are close to each other, i.e. CRSS { 110 } = ( 1.0 ± 0.1 ) × CRSS { 112 } . In all the tested specimens, the activation of the primary slip systems (e.g. systems that activate first) follows the Schmid's law. At first glance, the activation of secondary slip systems does not seem to comply with the highest Schmid factor. However, detailed investigation supported by crystal plasticity simulations reveals that the boundary constraints acting on the primary slip direction triggers an increase of the Schmid factors of the activated secondary slip systems, i.e. Schmid's law correctly justified all observed slip traces. Application of the found ferrite slip parameters in crystal plasticity simulations of ferrite-containing steels shows that correct input values are crucial for obtaining meaningful macroscopic predictions. [ABSTRACT FROM AUTHOR]