This classification is defined in Section 214.2(b) of the UCIS Operating Instructions.  "An alien member of a religious denomination coming temporarily and solely to do missionary work in behalf of that denomination if such work does not involve the selling of articles or the solicitation or acceptance of donations."  He/she also cannot work for a salary while in the U.S. This is probably the most widely used classification and it will continue to serve the purpose if the religious worker's country of citizenship is one where U.S. visas are relatively easy to obtain.  B-1’s are usually issued for six months and can be generally extended for an additional six months.  However, there is a little known problem with this classification.  We have emphasized it above.  Most missionaries speak in churches and conferences seeking to raise support and financial gifts for their work.  As you can see, the language of the Instructions strictly forbids that.  Even though UCIS does not always enforce it, a religious worker should not violate the requirements of their immigration classification.