Simultaneous communication, SimCom, or sign supported speech (SSS) is a technique sometimes used by deaf, hard-of-hearing or hearing sign language users in which both a spoken language and a manual variant of that language (such as English and manually coded English) are used simultaneously.

While the idea of communicating using two modes of language seems ideal in a hearing/deaf setting, in practice the two languages are rarely relayed perfectly. Often the native language of the user (usually spoken language for the hearing person and sign language for the deaf person) is the language that is strongest, while the non-native language degrades in clarity.

In an educational environment this is particularly difficult for deaf children as a majority of teachers who teach the deaf are hearing. Results from surveys in 1986 indicate that school professionals used signing with approximately 2/3rds of the population of deaf students, and that this signing is described by researchers in 1987 as "English-like."

Simultaneous Communication by hearing signers is criticized in the Deaf community because of the degradation of sign quality. It is believed that SimCom is performed for the benefit of a hearing audience and at the expense of the Deaf audience. As such, Deaf teachers often discourage the use of SimCom to their students.

Manual communication has existed as a major philosophy of Deaf education since the founding of the first formal Western school for the deaf in France by Charles-Michel de l'Épée in 1755, but Simultaneous Communication strategies gained mainstream traction in the United States in the 1970's. The history of using some form of sign language in the formal education of Deaf children, known as Manualism, has been a tumultuous one. In 1880, the Conference of Milan issued resolutions against both sign languages overall, and the use of Simultaneous communication.

"1. The Convention, considering the incontestable superiority of speech over signs, (1) for restoring deaf-mutes to social life, (2) for giving them greater facility of language, declares that the method of articulation should have the preference over that of signs in the instruction and education of the deaf and dumb. 2. Considering that the simultaneous use of signs and speech has the disadvantage of injuring speech and lip-reading and precision of ideas, the Convention declares that the pure oral method ought to be preferred."

The Milan resolutions were widely adopted by Western educational systems, especially in the United States, for much of the subsequent century. Schools for the deaf in the United States fired deaf teachers of the deaf (contributing to the overwhelming majority of hearing teachers of the deaf with significantly limited sign language training or experience) and banned the use of sign language in classrooms, including the use of corporal punishment for deaf students who used sign language with each other.

Following the failure of pure oralism to meet the needs of the deaf education system and its students, a number of philosophies to re-introduce manual communication in some form became prominent in the United States in the 1970s. The rise of SimCom is associated with the language planning movement in the United States towards the use of Manually coded language, specifically Manually coded English, which heavily modified existing ASL lexical items so that they could be matched to, and theoretically co-articulated with, spoken English utterances. SimCom was a major feature of Total communication, which was a collection of educational strategies and philosophies dedicated to integrating as many possible communication strategies in order accommodate students needing manual communication while continuing to emphasize spoken language.