It is now ten years since Hammersley and Welsh discovered (or invented) subadditive stochastic processes. Since then the theory has developed and deepened, new fields of application have been explored, and further challenging problems have arisen. This paper is a progress report on the last decade.
"Subadditive Ergodic Theory." Ann. Probab. 1 (6) 883 - 899, December, 1973. https://doi.org/10.1214/aop/1176996798