This work investigates the process underlying lexical blend formation. At first, we examine the concept of word in some linguistic models in order to find a definition which would accommodate compounding. Next, we present an overview of morphological and lexical compounding in Portuguese, including both traditional descriptions and those related to more recent linguistic theories. Then, the notion of lexical blend is introduced, according to the definitions presented by specialists in Portuguese Word Formation, and the traditional notion of lexical blend is confronted with the concept of lexical fusion. We then proceed to the analysis of a corpus of 106 occurrences of lexical innovation, selected from the work of the writer Mia Couto. The results of the analysis support the adoption of the concept of lexical fusion for all superposed constructions which are traditionnaly viewed as standard lexical blend cases. Our results also reveal the significant productivity of lexical fusion as a wordformation process in Portuguese, both in speech, where it had already been attested, and in written literary language. The analysis shows the adequacy of the concept of lexical fusion, defined as a systematic process of expressive predication of a word by another word whose phonological properties permit the felicitous operation of the process.