A wearable display could replace a laptop computer screen or serve as a mobile Internet browser, offering privacy, portability and hands-free operation. Although these and many other wearable display applications continue to excite the imaginations of product designers, the dream has yet to become reality. The main obstacles have been the cost of the display panel and the size and weight of the magnifying optics. With the emergence of microdisplay technology -- miniature high-resolution flat panel displays on silicon backplanes -- display panel costs are likely to drop to levels acceptable for consumer products. Now the challenge is to magnify the microdisplay image. The problem is to reconcile the very demanding requirements: extreme miniaturization with large exit pupils, wide fields of view and extreme off-axis imaging. Practical field-of-view requirements for data or video displays tend to push optical designs toward cumbersome solutions; in many cases, traditional optical design tools cannot meet the required form factors and optical system specifications. New optical elements such as electrically switchable holographic optics may offer the means to solve some tricky display magnification problems without adding weight or bulk.