Purpose: The aim of this paper is to elaborate on the opportunities and challenges to the application of portfolios as an assessment tool in English as a Foreign Language (EFL) classrooms at different educational levels in Vietnam, as explicitly and implicitly reported in the literature. Design: This study is a combination of a narrative review, synthesising educational documents during 2014-2021, and a systematic review, resulting in 26 empirical studies during 1999-2021 to be included. The adopted approach to data analysis was inductive, deductive and thematic. Data extracting and coding were conducted manually with the aid of Microsoft Word tools. Findings: The results indicate that enabling factors for the use of assessment portfolios included governmental documents; teachers' and/or students' awareness, attitudes and beliefs; available application of assessment portfolios and their benefits. However, practicality, reliability, validity and accuracy might pose certain challenges to this use. Value: This study adds further insights into our current understandings of the opportunities and challenges to the use of assessment portfolios in international EFL contexts.