YiddishDictionaryOnline.com is an online English to Yiddish dictionary, and the University of Kentucky also offers a free online Yiddish dictionary service for searching words, phrases and fragments in English or Yiddish. Google Books provides free samples of many Yiddish dictionaries,as well as their library and purchase locations.
Most public universities have Yiddish dictionaries in their catalogs; however, many of these dictionaries are outdated.
YiddishSlangDictionary.com is a free source for learning modern conversational and slang Yiddish terms and phrases. This site provides helpful tools such as flashcards, word history, interactive word usage quizzes and a downloadable mobile app for iPhone and Android.