The last two to three decades have seen significant advances in the mechanics of unsaturated soils. It is now widely recognized that the fundamental principles in soil mechanics must cover both saturated and unsaturated soils. Nevertheless, there is still a great deal of uncertainties in the geotechnical community about how soil mechanics principles well-established for saturated soils can be extended to unsaturated soils. There is even wide skepticism about the necessity of such extension in engineering practice (Sheng et al. 2013). This group discusses some common pitfalls related to the fundamental principles that govern the volume change, shear strength and hydromechanical behaviour of unsaturated soils. It also attempts to address the issue of engineering relevance of unsaturated soil mechanics.