Humberto Delgado Airport, in Lisbon, Portugal.

What is the difference between LIS and LPPT?

LIS is the IATA code, used commercially — tickets, timetables, luggage tags. LPPT is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.

What airport is LIS?

LIS is

Humberto Delgado Airport

Lisbon, Portugal

Why the code is LIS

The first three letters of Lisbon — the English name, not Lisboa.

The airport authority or a contemporaneous record states this directly.

The airport

IATA code: LIS
ICAO code: LPPT
Airport: Humberto Delgado Airport
City: Lisbon, Portugal
Code origin: Documented

Lisbon's airport is four miles from the centre and inside the city, which makes approaches unusually low over rooftops and makes expansion effectively impossible. Replacing it has been debated since the 1960s without resolution.

The other code, LPPT

Every airport has two codes. The three-letter IATA code, LIS, is the one on your boarding pass and your luggage tag, and it is assigned for commercial use. The four-letter ICAO code, LPPT, is the one pilots and controllers use, and it is assigned geographically: the first letter or two identify the region, so every airport in the same part of the world shares a prefix. That is why LPPT looks nothing like LIS.

Common questions

What airport is LIS?: Humberto Delgado Airport, in Lisbon, Portugal.
Why is Lisbon's airport called LIS?: The first three letters of Lisbon — the English name, not Lisboa.
What is the difference between LIS and LPPT?: LIS is the IATA code, used commercially — tickets, timetables, luggage tags. LPPT is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.

Portugal Capital, area, population and currency
The flag of Portugal Colours, symbols and lookalikes
Airport codes in Portugal 1 here

Sources

OurAirports — OurAirports (Public domain)

How these figures are compiled and checked