The importance of space for ecology and conservation relies on the importance of connectivity. It is well known that connectivity can influence populations and communities through a variety of mechanisms, and promoting connectivity is frequently championed as a way to mitigate negative effects of environmental change. Here, we provide an overview on the concept of connectivity and its relevance for applied ecology. We first outline the various interpretations regarding connectivity and theoretical developments that emphasize its importance. We then describe three general approaches to quantifying connectivity, including quantification based on structural features (i.e., structural connectivity) of the landscape, the use of spatially-explicit measures of connectivity based on the resistance of the landscape (e.g., potential functional connectivity), and the use of patch-based graphs (or network analysis) that quantify linkages between habitats. We illustrate how these approaches are implemented through two examples on endangered species. Our examples highlight different assumptions made in connectivity mapping, such as the use of least-cost paths and circuit theory, and how several patch-based graph metrics are related. We end by providing guidance for the advancement and applications of connectivity assessments.