Tarjan is known for his pioneering work on graph theory algorithms and data structures. Some of his well-known algorithms include Tarjan's off-line least common ancestors algorithm, and Tarjan's strongly connected components algorithm, and he was one of five co-authors of the median of medians linear time selection algorithm. The Hopcroft-Tarjan planarity testing algorithm was the first linear-time algorithm for planarity-testing.[8]
Tarjan has also developed important data structures such as the Fibonacci heap and the splay tree. Another significant contribution was the analysis of the disjoint-set data structure. He was the first to prove the optimal runtime involving the inverse Ackermann function.