This paper investigates the role of resource allocation in human sentence comprehension, proposing a simple information-theoretic characterization of processing difficulty as the work incurred by resource reallocation during parallel, incremental, probabilistic disambiguation. The theory is shown to be equivalent to Hale's (2001) surprisal theory, where the difficulty of a word is proportional to its *surprisal* (its negative log-probability) in the context within which it appears. This approach unifies findings on high-constraint contexts facilitating lexical processing and connects them to well-known models of parallel constraint-based comprehension. The theory leads to specific predictions about the role of expectation in syntactic comprehension, including the reversal of locality-based difficulty patterns in syntactically constrained contexts and conditions under which increased ambiguity facilitates processing. The paper examines established experimental results and shows that they are largely consistent with the surprisal theory, providing a unified framework for understanding various aspects of human sentence comprehension.This paper investigates the role of resource allocation in human sentence comprehension, proposing a simple information-theoretic characterization of processing difficulty as the work incurred by resource reallocation during parallel, incremental, probabilistic disambiguation. The theory is shown to be equivalent to Hale's (2001) surprisal theory, where the difficulty of a word is proportional to its *surprisal* (its negative log-probability) in the context within which it appears. This approach unifies findings on high-constraint contexts facilitating lexical processing and connects them to well-known models of parallel constraint-based comprehension. The theory leads to specific predictions about the role of expectation in syntactic comprehension, including the reversal of locality-based difficulty patterns in syntactically constrained contexts and conditions under which increased ambiguity facilitates processing. The paper examines established experimental results and shows that they are largely consistent with the surprisal theory, providing a unified framework for understanding various aspects of human sentence comprehension.