Abstract. We present a low-level coordination language for Haskell which can be used as an implementation language for parallel Haskell extensions. It has been developed in the context of the latest Eden implementation (based on the Glasgow-Haskell-Compiler, GHC, version 6) and it is thus referred to as the “EDen Implementation language”, EDI. EDI provides a small set of directly implemented primitive operations for basic thread control, system information, and communication. We explore the expressiveness and performance of both Eden and its low-level implementation language EDI in comparison. It turns out that hardly any differences in performance can be observed. The main advantage of EDI in comparison to Eden is more accurate control of parallel execution. Our long-term goals are maintenance and structured implementation of Eden and a solid low-level implementation language, which can be used for other parallel Haskells as well. 1