This thesis provides insight into the use of and variation in spoken West Frisian against the backdrop of the Frisian standard language and language contact with Dutch. Frisian is a minority language spoken in the Dutch province of Fryslân. It is predominantly a spoken language characterized by ample dialect variation. All Frisians are bilinguals and their language proficiency is often higher in Dutch than in Frisian. Spoken Frisian is known to be influenced by Dutch, but little is known about the actual linguistic variability of Frisian as used in everyday-life. The research reported in this book was conducted in the context of a larger study in Fryslân - a sociological language survey - which this PhD project is a part of. For the purpose of the two projects, an online questionnaire was developed that has been completed by 3.700 participants, varying in age (≥18 years old) and living in different parts of Fryslân. The questionnaire itself consisted of a sociological and a linguistic part. About 250 out of 3.000 Frisian-speaking participants who had completed the linguistic part of the questionnaire, were subsequently invited for an in-depth interview. The results confirm the wide-spread appearance of loanwords and loan constructions in spoken Frisian and its difference with regard to the Frisian standard, but they also show that language contact is a complex process, involving multiple factors. Not only can the borrowability of Dutch words and constructions strongly diverge, also their popularity and acceptance among the speakers varies extensively. With language knowledge and awareness actually exceeding the general assumptions, speakers of Frisian appear to make deliberate choices and adjust their language use to different interlocutors and situations.