On her deathbed, according to her secretary Alice B. Toklas, Gertrude Stein asked, "What is the answer?" Receiving no reply, she continued, "Then, what is the question?"

Human curiosity, and our insatiable impulse to ask questions, drives scientific research. In the July issue of Technology Review, readers had a chance to formulate their own list of the most important unanswered scientific questions. Presented with a list of 14 questions that Carnegie Institution president Maxine Singer and I claimed were among the most important in our book Why Aren't Black Holes Black? The Unanswered Questions at the Frontiers of Science, nearly 200 readers commented on the list by substituting their own favorite questions for ours. l Most of the respondees agreed with our premise that science, challenged by innumerable fascinating unanswered questions, is far from over. But many readers also identified what they they saw as serious ommisions and a few soundly denounced our list as misguided, elitist, or naive. In short, the survey demonstrated that while scientists are generally convinced that answers are achieved with some degree of objectivity, our choice of questions is highly subjective. Here are what Technology Review readers identified as the most compelling questions facing science today.