Codeswitching is a language-contact phenomenon which is characterized by the simultaneous use of the two languages of the bilingual and which has been used as a tool to investigate how these two languages interact in the mind of the bilingual. The present investigation focuses on English-Spanish codeswitching within Determiner Phrases (DP switches) and within copulative constructions with an Adjective Phrase (Adj switches). By following the minimalist premises proposed by MacSwan (1999MacSwan ( , 2000 and by Liceras et al. (2005Liceras et al. ( , 2008, two issues have been under consideration: (i) the directionality of the switch, and (ii) the gender agreement mechanisms in Spanish DP switches and in Spanish Adj switches (i.e., the analogical criterion, both [+AC] and [-AC], and the masculine as default). Experimental data have been collected via three experiments from two groups of L1 Spanish -L2 English bilingual speakers (i.e., children and adults): (i) an eyetracking during reading task, (ii) a reaction time task in Gorilla, and (iii) a visual world paradigm task. Thus, both offline and online experimental data have been elicited and analyzed, as well as compared to those in previous studies. Overall, regarding the directionality of the switch, the results indicate that English DP switches and English Adj switches are processed faster and are preferred. In the case of the gender agreement mechanisms, the results point to a hierarchy (i.e., [+AC] < masculine as default < [-AC]), which shows how strongly represented Spanish gender features are in the mind of these bilinguals for whom Spanish is their L1. However, children and adults show differences which could be attributed to (i) the complexity of the structure in terms of lexical access (i.e., Adj switches are more complex than DP switches), (ii) the type of data (i.e., different patterns are found depending on whether offline data or online data are considered), (iii) the implementation of the requirements imposed by feature strength (i.e., children's performance is affected when experimental conditions make the task harder), and (iv) the interplay between the three. Keywords: codeswitching; Spanish grammatical gender; DP switches; Adj switches; directionality of the switch; gender agreement mechanisms; offline and online data; children and adults; L1 Spanish -L2 English.