This volume presents a series of studies of an adult multilingual speaker who acquires a new language through social interaction. Five of the chapters have been published individually as articles at diverse places and are now gathered here together with an introduction and an added sixth chapter. They all emanate from a project conducted at Stockholm University which, as it matured, was named Processes in Third Language Acquisition.

This project started in 1990 when the young British linguist Sarah Williams arrived in Sweden to take up a job at Stockholm University and was faced with the need to learn Swedish. She saw this at the same time as an opportunity to document her progress in a new language from the outset. To this end, she and the present writer started to audio-record conversations in Swedish between the two of us at regular intervals in order to compile a longitudinal language corpus. This was continued for two academic years. During this time, we refrained from performing any analyses on the material, just aiming to bring together a broad corpus of semispontaneous conversational speech for later study. Sarah thus came to perform the methodologically rather unusual, but manifestly fruitful role of first serving as a language learner and supplier of data, and later, when the data collection was finished and her competence in Swedish was stronger, acting as a researcher of her own previous language performance together with the present writer.