Cost-effective integrated pest management of sea lampreys requires good assessment information. Assessment of sea lamprey populations is used to inform decisions about which control methods to use, as well as where and when to apply them. Additionally, assessment data are used to evaluate the performance of past management actions. This theme paper identifies key research questions that limit our understanding of sea lamprey population dynamics, as well as the quality of the assessment information currently used to inform management. The discussion is organized by dividing the sea lamprey life history into four stages—spawning, recruitment to age 1, larval, and parasitic—and examining the state of knowledge about population dynamics and assessment for each life stage. For spawning lamprey key research questions include migration timing, mating systems, and factors influencing spawning success. For recruitment to age 1, factors affecting recruitment variation and methods for age determination are critical needs. For larval lampreys, the primary target of control using lampricides, the key questions concern the accuracy of assessment methods used to guide lampricide treatment decisions and the effects of uncertainty on the utility of these methods. For parasitic lampreys, the main questions center on the nature of the host attack process and variation in survival during the parasitic phase. Finally, this review noted that the development of integrated models to evaluate control strategies remains a high priority for research. Because resources available for sea lamprey management are limited, high quality assessment information and good knowledge of sea lamprey population dynamics are key ingredients of a cost-effective control program.