Expanding legal access to medical cannabis across the United States increases availability and use of cannabis products to manage cancer-related symptoms and treatment side effects despite the lack of research-based evidence on its potential benefits and harms. To address knowledge gaps in how cancer patients access and use cannabis, their perceived risks and benefits with its use, and whether cancer patients discuss cannabis use with their healthcare providers during treatment, the National Cancer Institute (NCI) supported 12 NCI-designated comprehensive cancer centers to conduct surveys, which included NCI standardized core questions on cannabis use during treatment, among their cancer patient populations. This overview highlights key results from the articles contained in the monograph, which includes a summary of the results of core questions across all centers and reports from individual or groups of cancer centers on survey results related to the sourcing of cannabis, associated cost, behavioral factors associated with cannabis use (such as smoking, drinking, or using other substances), patient-provider communication on cannabis use during treatment, ethnic variations in patterns, sources, and reasons for cannabis use as well as methodologic concerns related to survey data analysis. The results of these surveys of cannabis use after the diagnosis of cancer lay the groundwork for much-needed research to answer the questions of benefits and harms, including potential interactions with cancer treatments for cancer patients.