This thesis presents a corpus of beginning learner German with a reliable error annotation scheme and an approach for detecting and diagnosing grammatical errors in learner language. A constraint-based dependency parser provides the foundation for a flexible and modular analysis of German by representing parsing as a constraint satisfaction problem. The grammar checker, Fledgling, detects and diagnoses errors using constraint relaxation with a general-purpose conflict detection algorithm. Fledgling is developed and evaluated using authentic learner productions from the learner corpus. It judges grammaticality correctly for 80% of sentences and is 82-91% accurate in determining whether a sentence contains selection, agreement, or word order errors. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]