A ‘modern classic’ of Portuguese variational linguistics suggests to us that O Português são dois (Mattos e Silva 2004). This title – borrowed from Carlos Drummond de Andrade’s poem Aula de Português – verbalizes a linguistic reality not only evident to scholars, but equally intuitive to non-linguist speakers of Brazilian Portuguese (BP) alike: unmonitored BP of communicative immediacy in the sense of Koch/Oesterreicher (1985) differs considerably from the Portuguese taught in Brazilian schools. Simplifying a great deal at this point, the latter – but not the former – is mostly based on an exogenous and idealized norm of European Portuguese (EP). In other words, a good deal of the “catchiness” of O Português são dois ultimately also resides in its alluding to a striking number of salient (and not so salient) properties that distinguish BP from EP. […] While elsewhere emphasis on theoretical differences has led to a stronger separation between research groups of different theoretical persuasions, (Brazilian) Portuguese linguists have found a unique way to achieve a fruitful collaboration between the two major approaches to linguistic variation, i.e. traditional sociolinguistics and the generative Principles and Parameters Model (cf. Kato 2006). In addition, a third model is currently gaining ground in Brazil, namely a complex systems approach (Castilho 2007, this volume). Given previous experience with the two more traditional approaches, it seems desirable to extend this dialog and mutual exchange of ideas and results to the complex systems approach. The present volume therefore brings together studies which make use of all three approaches.