The four papers in this special issue deal with the acquisition of morphology and semantics in the nominal domain in two groups of language learners: adult second-language (L2) learners (Sagarra & Herschensohn; Cuza, Guijarro-Fuentes, Pires, & Rothman) and simultaneous bilin- gual children (Eichler, Jansen, & Muller; Larranaga & Guijarro-Fuentes). The acquisition of gender is the focus of three of the papers, while the fourth explores the interpretation of plural noun phrases in specific and generic contexts. Romance (Italian, French, and Spanish), Germanic (English and German), and a non-Indo-European language (Basque) form the empirical basis of the four studies. Despite the different language populations and the different aspects of the nomi- nal domain under investigation, the articles share some theoretical concerns that will be explored in the following.Two main issues cut across the articles on the acquisition of gender: the inevitable question about differences and similarities between bilingual and monolingual speakers, and the nature of what it is that language learners actually need to acquire. As for the two papers on adult L2 learn- ers, the additional issue revolves around evidence for acquisition of L2 features that are not present in the first language (L1), and the degree to which learners can achieve native-like competence as a function of experience. The role of input is also explored in the article by Eichler et al. in terms of language dominance in bilingual children. Another theme that is at the forefront of the article by Sagarra and Herschensohn is the relationship between representation and computation and the extent to which extra-linguistic factors, such as working memory capacity, affect the online com- putation of gender.Similarities and differences between bilinguals and monolingualsOne of the items high on the agenda of bilingual research is the extent to which the linguistic behavior of bilinguals is similar or different from monolinguals'. In developmental terms this begs the question of how exposure to two languages affects the course of language acquisition; factors such as the quantity and quality of the input (e.g. Argyri & Sorace, 2007; Cornips & Hulk, 2006; Paradis & Navarro, 2003; Pearson, Fernandez, Lewedeg, & Oller, 1997; Sorace, Serratrice, Filiaci, & Baldo, 2009; Thomas & Gathercole, 2007), and the age at which children are first exposed to two languages (e.g. Meisel, 2008, 2010; Unsworth, 2008; Unsworth & Hulk, 2009) have been shown to play a role. The age of exposure is controlled for in the Eichler et al. and in the Larranaga and Guijarro-Fuentes papers, as the children are all simultaneous bilinguals who have been regu- larly exposed to two languages from birth. There is, however, variation in terms of children's lan- guage dominance in the Eichler et al.'s study that is related to the marking of gender in their weaker language. The issue of language dominance is not explicitly linked by the authors to the quantity and quality of the input addressed to the children, rather it is considered for the cascading effect that it has on the accuracy of gender marking. The case made by the authors is that although devel- opment in the weaker language can be slower, it does not necessarily mean that children are less accurate. Two of the children in their sample are reported to have a mean difference between the Mean Length of Utterance (MLU) values in their two languages of almost two words and as a result are classified as unbalanced bilinguals. Both children are, however, surprisingly accurate in German, their weaker language. The authors nevertheless point out that this superficially impres- sive performance betrays a low degree of lexical diversity with a small number of gender-marked noun types in the children's lexicon. Lexical conservatism is a trade-off for their relatively error- free use of gender marking; in more general terms, this could be viewed as an indication of low productivity and, therefore, call into question these children's overall acquisition of the complex gender system of German. …