Brain tumors rank second as the cause of cancer-related deaths in children and adults younger than 34 years old, and they are seen in adults of all ages. Primary malignant brain tumors are associated with the third highest cancer-related mortality rate and a disproportionate level of disability and morbidity. Considering this, accurate diagnosis and grading of brain tumors are critical to determining prognosis and therapy. Equally important is to evaluate for tumor status during therapy to assess for therapeutic response and treatment-related complications. Brain tumors can be characterized as a heterogeneous group of neoplasm with a correspondingly wide variation in malignant phenotype and a diverse array of imaging features. Magnetic resonance (MR) imaging with intravenous contrast agent is the test of choice to diagnose and monitor brain tumors before, during, and after therapy. Recent advances in imaging methods such as diffusion-weighted imaging, perfusion imaging, and spectroscopic imaging all have in common the ability to provide quantitative cellular, hemodynamic, and metabolic information that may enhance our understanding of brain tumor biology, help us to better assess treatment response, more accurately determine tumor activity during therapy, and differentiate recurrent tumor and treatment related complications. In this article, we will review the basics of brain tumor imaging and focus on the role of perfusion MR imaging in improving accurate diagnosis and monitoring brain tumors during therapy. Both strengths and shortcomings of perfusion MR imaging over standard anatomic MR imaging will be discussed as will important pitfalls of the technique.