An I-94 is a form denoting the Arrival-Departure Record of particular foreigners used by U.S. Customs and Border Protection (CBP). U.S. Citizenship and Immigration Services (USCIS) uses Form I-94 also. Form I-94 must be completed at the time of entry to the United States by foreign citizens that are being admitted into the United States in a nonimmigrant visa status. While citizens of the countries in the U.S. Visa Waiver Program (VWP) list, who are entering the United States via an air or seaport for 90 days or less and who are not U.S. citizens or permanent residents are required to complete an I-94W ("Nonimmigrant Visa Waiver Arrival/Departure Form"), these visitors must now also obtain an Electronic System for Travel Authorization (ESTA) prior to traveling to the United States. The I-94W form requirement has been dropped during Summer 2010, after a transitional period, for VWP applicants. A completed Form I-94 is presented by the foreign citizen at the port of entry to the United States to a CBP Officer, who stamps the form and gives the final approval for admission of the foreign citizen into the United States in a specific nonimmigrant status for a specific authorized period. As a general rule, non-U.S. citizens who are also non-U.S. permanent residents departing the United States are required to surrender their Form I-94 when leaving the United States, so that their departure can be properly recorded by the CBP Officers (typically to the airline or ship representative, or into a deposit box in the terminal). If the Departure Record portion is not surrendered then it may cause difficulties trying to re-enter the USA, as the systems used to track ingoing and outgoing visitors may show that the holder has overstayed, although this may be rectified. When departing the United States for Canada or Mexico (only), for a trip of less than 30 days, it is not required to surrender the I-94 If the I-94 form is lost or stolen while the nonimmigrant is in the United States, a replacement form may be requested from USCIS. While in the United States, non-immigrant visitors (but not VWP visitors) may apply for a change of non-immigrant visa status from one category to another or for an extension of the previous nonimmigrant status by filing form Form I-539 with USCIS. Upon approving such application, USCIS issues an approval notice, the bottom portion of which is a new Form I-94 for the nonimmigrant, reflecting that visitor's new or extended non-immigrant visa status and also showing a new authorization period for that status. The I-94 paper form is no longer required for international visitors arriving by sea or by air. Instead, arrival and departure information is gathered electronically from carriers. Visitors can verify immigration status or employment authorization, as well as record number and admission information at "https://i94.cbp.dhs.gov/I94/request.html". This system shift was scheduled to go into effect at 5 airports (Charlotte, Chicago, Las Vegas, Miami, and Orlando) from April 30, 2013, and progressively introduced at other major ports of entry during the following three weeks.