Context. Agile Software Development has provided a new concept of Software Development based in adaptation to changes, quick decisions, low high-level design and frequent deliveries. However, this approach ignores the value that Software Architecture provides in the long term for increasing the speed in delivery working software, which may have catastrophic consequences in the long term. Objectives. In this study, the combination of these two philosophies of Software Development is investigated. Firstly, the concept of Software Architecture in Agile Projects; then, the major challenges faced concerning Software Architecture in Agile Projects, the practices and approaches that can be used to overcome these challenges and the effects that these practices may cause on the project. Methods. The research methodologies used in this study are Systematic Literature Review for gathering the highest amount possible of contributions available in the Literature at this respect, and also the conduction of Semi-Structured Interviews with Agile Practitioners, in order to obtain empirical knowledge on the problem and support or deny the SLR findings. Results. The results of the Thesis are a unified description of the concept of Software Architecture in Agile Projects, and a collection of challenges found in agile projects, practices that overcome them and a relation of effects observed. Considering the most frequent practices/approaches followed and the empirical support, it is enabled a discussion on how to combine Software Architecture and Agile Projects. Conclusions. The main conclusion is that there is not a definite solution to this question; this is due to the relevance of the context (team, project, customer, etc.) that recommends the evaluation of each situation before deciding the best way to proceed. However, there are common trends on the best-recommended practices to integrate these two concepts. Finally, it is required more empirical work on the issue, the conduction of controlled experiments that allows to quantify the success or failure of the practices implemented would be most helpful in order to create a body of knowledge that enables the application of certain practices under certain conditions.