Buckling of piles is prevented by the surrounding soil. Therefore, in sufficiently stiff soils, there is no risk of pile buckling with conventional geometry (L/D ratio). National and international design codes require checks of the safety against buckling for slender piles in soils with undrained shear strengths of cu < 15 kPa or cu < 10 kPa, respectively. In practice, the codes imply that buckling failure does not occur at higher undrained shear strengths. However, using simple calculations, this assumption has been proven to be invalid for slender piles such as micropiles. For the reason, buckling tests on 4 m long micropiles were carried out in soft clay. Based on these results, a new concept with supporting documents for calculating buckling loads was derived, which covers all essential aspects observed in the tests. The proposed model accounts for material non-linearity, as well as second order effects.