The concept of nanotechnology embraces a vast spectrum of existing and anticipated capabilities. At the one end of the spectrum are today's laboratory capabilities in chemistry, protein engineering, lithography, and scanning probe microscopy. Toward the far end of the spectrum are anticipated capabilities based on advanced molecular assemblers and design systems. Crossing the gap between the actual and the foreseeable will require increases in the sizes, frequencies, accuracies, and reliabilities of nanosystems, and in their structural complexities. Several of the required improvement ratios are in excess of a billion. A survey of long-term objectives and milestones can help us in setting directions for current research.