A computer-implemented method performed by a data processing apparatus, the method comprising: receiving audio data that corresponds to an utterance; obtaining (i) a first transcription of the utterance from a first one of a mobile computing device and a server computer device and (ii) a second transcription of the utterance from the mobile computing device or the server computing device; wherein the first transcription was generated using a limited speech recognizer, the limited speech recognizer comprising a speech recognizer that includes a language model that is trained over a limited speech recognition vocabulary that includes one or more terms from a voice command grammar, but that includes fewer than all terms of an expanded grammar; and wherein the second transcription was generated using an expanded speech recognizer, the expanded speech recognizer comprising a speech recognizer that includes a language model that is trained over an expanded speech recognition vocabulary that includes all of the terms of the expanded grammar; processing the first transcription and second transcription to determine a grammatical alignment between the first transcription and the second transcription; analyzing the aligned transcriptions to determine the type of utterance as being a voice action command or a voice search command and what transcribed words are to be used to execute the command; associating each word or phrase within the first transcription and the second transcription with a confidence score and/or weight reflecting a likelihood of relevance within the context of a voice action or voice search for each word or phrase within the first transcription and the second transcription; comparing the confidence scores and/or weights of corresponding pairs of words or phrases from the first transcription and the second transcription to determine a combined transcription that represents the utterance; and providing the combined transcription to a voice action engine when the utterance is identified as being a voice action and providing the combined transcription to a search engine when the utterance is identified as being a voice search. receiving audio data that corresponds to an utterance; obtaining (i) a first transcription of the utterance from a first one of a mobile computing device and a server computer device and (ii) a second transcription of the utterance from the mobile computing device or the server computing device; wherein the first transcription was generated using a limited speech recognizer, the limited speech recognizer comprising a speech recognizer that includes a language model that is trained over a limited speech recognition vocabulary that includes one or more terms from a voice command grammar, but that includes fewer than all terms of an expanded grammar; and wherein the second transcription was generated using an expanded speech recognizer, the expanded speech recognizer comprising a speech recognizer that includes a language model that is trained over an expanded speech recognition vocabulary that includes all of the terms of the expanded grammar; processing the first transcription and second transcription to determine a grammatical alignment between the first transcription and the second transcription; analyzing the aligned transcriptions to determine the type of utterance as being a voice action command or a voice search command and what transcribed words are to be used to execute the command; associating each word or phrase within the first transcription and the second transcription with a confidence score and/or weight reflecting a likelihood of relevance within the context of a voice action or voice search for each word or phrase within the first transcription and the second transcription; comparing the confidence scores and/or weights of corresponding pairs of words or phrases from the first transcription and the second transcription to determine a combined transcription that represents the utterance; and providing the combined transcription to a voice action engine when the utterance is identified as being a voice action and providing the combined transcription to a search engine when the utterance is identified as being a voice search.