Abstract: Systems and methods are disclosed enabling recommendations of content items based on a difficulty of the content item as well as a skill level of the user. Skill-based content recommendations may be utilized, for example, in recommending content to language learners. Skill-based recommendations may be based on a variety of difficulty metrics of the content item, such as vocabulary and complexity of the language (e.g., words per paragraph, syllables per word, etc.), as well as a variety of skill metrics of the user (e.g., as explicitly provided by the user or implicitly determined based on a user's interaction with content items). Advantageously, such metrics can enable generation of recommendations based on a multi-dimensional difficulty assessment. Further, difficulty metrics, skill metrics, or the relationship between such metrics may be dynamically updated over time based on continued feedback from users, such that recommendations are dynamically improved.