The currency in Laos is the Kip (LAK) which comes in 5,000, 2,000, 1,000, 500, 100 and 50 Kip denominations. In most travel destinations, with the exception of the remote or mountainous areas, Thai Bahts and US Dollars are also accepted widely. For items of higher prices such as room rates at luxury hotels, food at first class restaurants, deluxe tour packages...the prices are normally quoted in US Dollars.

You can convert US Dollars or Thai Baht into the local currency as much as possible upon entry. But having some cash in US Dollars, some in Thai Baht and some in Lao Kip is recommended. The more expensive items quoted in US Dollars should be paid in US Dollars and the others should be either in Thai Bahts or in Lao Kips, otherwise you will not have as good rates as should should. While US Dollars is convenient for carrying, Thai Bahts and Lao Kips may be bulky and not convenient while you are travelling.

Make sure that you spend all of your cash in Kips before leaving Laos, as the currency become almost useless outside of the country. You can convert Lao Kips into US Dollars or Thai Baht at many local banks with a small fee.

If your trip involves travelling in remote areas, it's better to be prepared with plenty of Lao Kips or Thai Bahts, the latter is preferred since it's more convenient. The reason is that in many remote areas, US Dollars is not preferred and either not accepted or accepted for a very low exchange rate. Also you should always be armed with some Kips for daily small items such as drinks, fruits...

 There are many local banks, foreign banks and money changers in most major towns of Laos. The exchange rate is normally better at the banks than at street money changer. But changing money at street money changer is more convenient as they open on public holidays, at weekends and they are open for longer hours than banks.
 Credit cards in US Dollars are excepted at up-class hotels and restaurants in Vientiane and Luang Prabang. But normally advances/withdrawals can only be in Kips and not US Dollars. There's a fee for withdrawing money from your credit card account or paying for your expenses by credit card. If you plan to travel to remote areas, be prepared with enough cash, preferably in Thai Baht or Lao Kips for the safe side.
 
 Traveller cheques are not normally excepted in Laos, except for a limited number of banks in Vientiane and Luang Prabang. If you plan to bring traveller cheques, then buy them in US Dollars and Vientiane is the place to cash.

There's virtually no ATMs in US Dollars at the time of writing in Laos. When travelling, make sure you have enough money in cash for weekends.