In situ processing is playing an increasingly prominent role in visualizing and analyzing data on HPC platforms. In this presentation, I will cover three major themes. First, I will discuss the trends on HPC platforms that make in situ processing increasingly attractive compared to post hoc processing. Second, I will discuss the diversity of approaches that all fall within the in situ theme, with respect to axes such as data access, proximity, division of resources, etc. Third, I will discuss the opportunities inherent to in situ processing, and why this paradigm may allow us to do better science than we could previously.