Does darkness lead to happiness? Is there corn in the corner? These are questions that make - to some extent - semantically sense, but for researchers interested in the role of morphology in word processing they make morphologically sense as well. This Special Issue on Morphological Processing is based on the 6th MOrphological PROcessing Conference MOPROC, which was organized in Turku, Finland and hosted researchers with a firm interest in questions like these. The special issue contains 13 articles that provide answers from different viewpoints, since it contains research on comprehension, production, and acquisition of morphology. Moreover, the articles present research in a number of languages with fundamentally different morphological systems. Apart from studies in West-Germanic languages (English and Dutch), the special issue contains studies in Romance languages (Spanish and Italian), in languages with very rich inflectional paradigms (Greek, Polish and Finnish) and in languages with non-concatenative morphology (Hebrew and Arabic). Moreover, it contains studies on all three major morphological classes: Inflections, derivations and compounds. Specific questions addressed in the volume deal with the time course with which morphemes come available, what factors facilitate their use, the role of orthographic and semantic transparency in complex word processing and how morphology should be incorporated in models of word processing. The chapters provide a wealth of empirical results obtained with state-of-the-art experimental paradigms. We hope that they will be an inspiration for further studies in morphological processing as much as we - living in Finland - hope that there is happiness in darkness.