The domain of social media and social network sites is a comparatively new and extensive phenomenon in today’s society. Since their introduction, social network sites, such as Facebook, Instagram, and Twitter have attracted millions of users and are distinguished as an element of immense time consumption in many people’s lives. This thesis investigates the use of Instagram, a social network site where users are able to share pictures, videos and texts with the community. The main focus of the study is the analysis of the relationship between language, gender, and identity building in this social network. Previous research has tackled many different aspects of social media related to gender and identity. However, the focus has mainly been on the general area of images and language devoid of finding specific connections between the authors behind the analyzed materials. Therefore, this study adds to previous studies by also integrating the focus of a specific field in the analyses, that of fitness as a lifestyle. To collect the data, a number of well-known English-speaking fitness bloggers were selected from different countries including Venezuela, Colombia, Germany, France, Australia, Puerto Rico and the USA. In order to analyze the data, multimodal discourse analysis is incorporated using the theory of systemic functional linguistics, developed by Halliday (1994), including ideational, interpersonal, and textual metafunctions. Conclusively, although certain posts appear to be ‘more masculine’ than others, there are many similarities in the use of language by both men and women. The language used in men and women’s posts does not differ vastly contingent on the gender of the bloggers.