The article identifies the validity of assessment of non-formal and informal learning achievements (NILA) as one of the key factors for encouraging further development of the process of assessing and recognising non-formal and informal learning achievements in higher education. The authors analyse why the recognition of non-formal and informal learning achievements is still being accepted rather sceptically in higher education and discuss whether these achievements can be recognised at all and what principles are followed in order to achieve valid and reliable assessment. The article reviews several models for the assessment and recognition of non-formal and informal learning achievements that could possibly be used by universities and colleges. The authors discuss what assessment methods are used in different models. Models that emphasise assessment of non-formal and informal learning achievements are formative. Thus the key method of assessment is portfolio. The aim of these models is qualification recognition and accreditation. Irrespective of the type of the assessment and recognition model of non-formal and informal learning achievements used in a higher education institution, it is very important to assure the quality of this process and to note that credit award models dominate in contemporary higher education institutions. Once adapted to formal criteria of study programmes at higher education institutions, these models are the most appropriate tool for comparing and recognising non-formal and informal learning achievements.