The expanding use of scientific balloons as a cost-effective alternative to orbital and suborbital space flight has driven the development of ultra-high altitude balloon (UHAB) vehicles. Of particular interest is the ability to fly payloads approaching 900-1000 kg to altitudes in excess of 45 km using traditional zero-pressure designs. A zero-pressure balloon of nearly 1.7 million cubic meters (60 million cubic feet) volume was developed for NASA and launched in Summer 2002. This was the largest balloon ever successfully flown, reaching an altitude of 49 km. Presented in this paper is an overview of the design and material challenges involved in developing large ultra-high altitude balloons, as well as a summary of the Summer 2002 test flight. In addition to providing unprecedented altitudes from which to make scientific observations, the UHAB also opens new avenues for long duration ballooning at mid-latitudes. With altitude excursions of 10-12 km, these balloons will be able to execute long duration flights without the need for large quantities of ballast. If augmented by a small superpressure anchor balloon, the altitude excursions could be kept to a minimum. While not as capable as the ultra long duration balloon (ULDB) in carrying large payloads, the UHAB would add another capability for scientists with relatively light payloads who desire to maximize mission time and altitude.