Type checkers are invaluable tools which help programmers write correct programs. Fast and efficient type checkers are required to enable adoption of such tools in practice. This study aims to provide an explorative overview of proposed efficiency improvements for type checkers. This provides language implementers insight in what approaches exist to increase the performance of their type checker. Efficiency improvements are divided into three general approaches: incrementalization, parallelization, and algorithmic improvements. For each category, we discuss the implementation techniques and performance for several proposed approaches. This study finds that a wide variety of approaches exist to increase the efficiency of type checkers. Based on reported benchmark results, incrementalization and parallelization are promising approaches to writing fast type checkers.