From GoToCayman.com - the Wiki for Cayman
US, British and Canadian citizens, and citizens of British Dependent Territories do not require passports, but must present proof of citizenship (passport or birth certificate and current photo ID). Originals of documents must be presented; photocopies are not acceptable. A driver's license or voter's registration card alone is not sufficient. You must also have a return or ongoing airline ticket.
Note: Under the Western Hemisphere Travel Initiative regulations, from 23rd January 2007 all travelers entering the US (including US citizens) from Canada, Mexico, Central and South America, the Caribbean, and Bermuda by air will be required to hold a passport. Currently cruise passengers will need to have a passport by January 2008, but press reports indicate that this will be postponed to June 2009. For full details see the US State Department website at http://travel.state.gov/travel/cbpmc/cbpmc_2223.html
Visitors from all other countries require a passport and return or ongoing ticket. Entry is granted for up to six months. Resident aliens of the US who show a valid US Alien Registration Card (green card) may be permitted to enter and remain in the Cayman Islands for up to 30 days. You must keep the pink Immigration slip given to you upon arrival! This is their equivalent of a tourist identification card. Visitors should keep it with their travel documents and present it when departing. Anyone who wishes to extend their stay after arrival must visit the Department of Immigration and obtain an extension and may be asked to show proof of financial resources to permit an extension.
Visitors may have to prove they have sufficient funds to support themselves and their dependents and have tickets to their next destination. Visitors may be refused entry if their appearance or behaviour do not meet the normal social standards of Cayman.
Visitors may not engage in any form of employment without additional authority (ie a work permit). Prohibited immigrants include the destitute, health hazards to the community, prostitutes, those living on prostitution, the previously deported, anyone sentenced to over a year's imprisonment and others proscribed as undesirable for moral or economic reasons.
NOTE: From 1st November 2005 residents from Costa Rica, El Salvador and Guatemala, and Jamaica will join some 112 other countries whose nationals are presently subject to visa requirements. Persons travelling on documented, valid work permits will not require visas for entry or reentry. The process for applying for visas is given on the Cayman Islands Immigration Board website at http://www.immigration.gov.ky/portal/page?_pageid=1608,2524716&_dad=portal&_schema=PORTAL. Note that there are special procedures for Jamaican nationals who want to visit Cayman - these are also on the above page.
A full list of country nationals that do not require visas is on the official Cayman Islands Department of Tourism website at http://www.caymanislands.ky/getting%5Fthere/entry_requirements.aspx. On the Cayman Islands Immigration Department website at http://www.immigration.gov.ky/ there is more comprehensive information on the visa process, including a downloadable visa application form.