We know surprisingly little about how professional developers define debugging and the challenges they face in industrial environments. To begin exploring professional debugging challenges and needs, we conducted and analyzed interviews with 15 professional software engineers at Microsoft. The goals of this study are: 1) to understand how professional developers currently use information and tools to debug, 2) to identify new challenges in debugging in contemporary software development domains (web services, multithreaded/multicore programming), and 3) to identify the improvements in debugging support desired by these professionals that are needed from research. The interviews were coded to identify the most common information resources, techniques, challenges, and needs for debugging as articulated by the developers. The study reveals several debugging challenges faced by professionals, including: 1) the interaction of hypothesis instrumentation and software environment as a source of debugging difficulty, 2) the impact of log file information on accurate debugging of web services, and 3) the mismatch between the sequential human thought process and the non-sequential execution of multithreaded environments as source of difficulty. The interviewees also describe desired improvements to tools to support debugging, many of which have been discussed in research but not transitioned to practice.