TLI may refer to:

• Thallium(I) iodide, a Thallium compound

• Transport Layer Interface, a networking application programming interface.

• Trans-lunar injection, a propulsive maneuver used to set a spacecraft on a trajectory which will arrive at the Moon.

• Tseng Laboratories, Inc., the full corporate name of Tseng Labs

• Tall Latte index, an economic index based on the cost of a cup of Starbucks coffee

• Taipei Language Institute, an institute for teaching Mandarin Chinese founded in 1956

• The Lonely Island, an American comedy troupe

• The Living Infinite

• Trophic level index, an index used in New Zealand for measuring the nutrient content of a lake

• Term Life Insurance

• Temporal light interference, undesired degradation or malfunction of an equipment or system caused by light modulations