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Published in Agron. J. 103:1645–1654 (2011) Posted online 14 Sep 2011 doi:10.2134/agronj2011.0131 Available freely online through the author-supported open access option. Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. T first use of hops—with the tender shoots and young leaves used as a salad (Burgess, 1964)—was described in the fi rst century A.D. in Pliny’s Natural History. Th e earliest records of hop cultivation date back to the 8th century, when French and German monks grew hops, presumably for their medicinal value (Burgess, 1964). Hops have a long history of use for medicinal purposes, and they have most oft en been used as a mild sedative due to their anti-anxiety properties. It was not until the 12th century that hops became widely used as a preservative and clarifying component in the beer-brewing process (Burgess, 1964). Hop cultivation and brewing have been an important part of American culture since the fi rst colonists arrived. By the mid1600s, widespread cultivation of hops was becoming commonplace, with farms up to 18 ha in size. Hop production had spread from New York to Wisconsin, and fi nally to the Washington Territory and California by the late 1800s (Steiner, 1973). Th e Humulus genus is made up of dioecious (rarely monoecious), perennial, short-day fl owering plants of the family Cannabaceae and is indigenous to northern temperate climates (Mahaff ee and Pethybridge, 2009; Small, 1978). Th e Humulus genus has three distinct species: H. japonicas Siebold & Zucc., H. yunnanensis Hu, and H. lupulus L. Humulus japonicas is an annual species native to China, Japan, and Taiwan and is cultivated primarily for its ornamental value. It has been introduced to Europe and North America and is now considered a semi-invasive species in some areas of the eastern United States (Mahaff ee and Pethybridge, 2009). Humulus yunnanensis is a relatively unknown species thought to have originated at high elevations in the Yunnan province of southern China (Mahaff ee and Pethybridge, 2009). Humulus yunnanensis is not widely cultivated, and, according to Small (1978), is oft en confused with H. lupulus, while other, more recent sources report that it is a rare species (Mahaff ee and Pethybridge, 2009). Humulus yunnanensis is not found in the USDA’s national plant germplasm system (Mahaff ee and Pethybridge, 2009). Humulus lupulus, widely known as the common hop plant, is the species that possesses marketable traits used for brewing. It consists of a number of taxonomic varieties: H. lupulus var. neomexicanus A. Nelson & Cockerell adapted to western cordilleran conditions; H. lupulus var. cordifolius (Miguel) Maximowicz distributed in eastern Asia, most notably Japan; H. lupulus var. pubescens E. Small of the Midwestern United States; H. lupulus var. lupuloides E. Small of eastern and central North America; and H. lupulus var. lupulus, which originated in Europe but has spread to Asia, Africa, and eastern North America and is the taxonomic variety responsible for retaining most of the favorable brewing characteristics (Hampton et al., 2001; Mahaff ee and Pethybridge, 2009). One other taxonomic variety, H. lupulus var. fengxianensis J.Q. Fu, has also been described (Peredo et al., 2009). Overlapping and introgression is evident for some varieties (Mahaff ee and Pethybridge, 2009). Th ough wild hops cannot be used directly for brewing due to ABSTRACT Hop cones grown on the female plant of the perennial crop (Humulus lupulus L.) are an integral component of the brewing process and provide fl avor, bitterness, aroma, and antimicrobial properties to beer. Demand for organically grown hops from consumers via the brewing industry is on the rise; however, due to high N requirements and severe disease, weed, and arthropod pressures, hops are an extremely diffi cult crop to grow organically. Currently, the majority of the world’s organic hops are grown in New Zealand, while other countries, including China, are beginning to increase organic hop production. Land under organic hop production in Washington State, where 75% of the hops in the United States are grown, increased from 1.6 ha to more than 26 ha from 2004 to 2010, and other hop-producing states demonstrate a similar trend. Removing hops from the USDA Organic Exemption list in January 2013 is expected to greatly increase organic hop demand and will require corresponding increases in organic hop hectarage. Current challenges, including weed management, fertility and irrigation management, insect and disease pressures, and novel practices that address these issues will be presented. Here, we discuss current and future research that will potentially impact organic hop production in the United States.