This popular helicopter has its origins in the MBB Bo-108, that was a technology demonstrator developed in the late 1980s by MBB and Aérospatiale. By 1995 the conventional open tail rotor had been replaced by a shrouded one (or fenestron) and both companies had gone up in Eurocopter. Hence the helicopter was re-designated EC135. Later, when Eurocopter became Airbus Helicopters, the EC135 was given marketing name H135.

The EC135 has a very streamlined fuselage that includes the majority of the engine and gear bix housing. Even the air intakes and exhausts of the two engines are nearly flush with the fuselage. On top is still a small pylon with the four blade, hinge-less main rotor directly above. Up front are curved cockpit windows and the helicopter has three side windows (including one in the cockpit door), that have a smaller height further aft. The rear fuselage sloes up quickly, allowing easy access to the cabin via clamshell doors. Above these doors is the slender tail boom ending in a big tail with large shrouded tail rotor. The horizontal stabilisers are just in front of the tail rotor. The EC135 can be equipped with low of high skids.

The different versions of the EC135/H135 family can be recognised by looking at:

• the number, size and location of air intakes on top of the fuselage
• the presence of end plates at the horizontal stabilisers
• the presence of a bump below the fenestron (tail rotor)

The EC135 has two engine options, one from Pratt & Whitney (models with suffix P) and one from Turbomeca (models with suffix T). However, the engine type does not lead to an external difference, except maybe for a sticker of the manufacturer. P2, P2+, T2 and T2+ have updated engines and/or MTOW increases. The plus-models are marketed as EC135P2i, EC135P2e, EC135T2e or EC135T2i. Some late plus models already seem to have the revised air intakes of the H135, but still have vertical fins at the ends of the horizontal stabilisers.

The Japanese navy uses the EC135T2+ for training purposes. It is designated TH-135 over there.

EC635 is the designation for the dedicated military version of the EC135. It is externally the same as the EC135; the main difference is in the re-inforced structure, especially the floor.

Like all helicopters of Eurocopter the EC135 got an Airbus marketing name. This was done from the EC135P3/T3 on. The H135 can be distinguished from the earlier models by the air intake at the side of the cowlings, smaller (cooler) at the front and an additional intake at the rear of the small pylon directly underneath the main rotor. Furthermore the horizontal stabilisers have no end plates anymore. Finally, on most H135s the bump below the tail rotor is gone, but there may be older versions without it as well.

H135M is the dedicated military version of the H135, but not recognisable from the civil H135.

In British military service the H135 (not H135M) is known as Juno HT1. The Brazilian navy operates H135Ms as UH-17.