The Lao language is a member of the Tai language group, sometimes known as Tai-Kadai or Kadai.  Thai is well understood in Laos, since Lao people will watch Thai television and listen to Thai radio. Many of the goods that you will see in Laos are imported from Thailand.  The north eastern part of Thailand, known as Issan has in fact more Lao speakers than Laos itself.

Lao is a tonal language, with six tones - most people will find it quite hard to differentiate between the tones, but any attempt to speak just a few words will win you instant friends.