The single-aisle airliner market is one of the most lucrative and hotly contested segments in the aviation business. But for the past 15 years, that white-hot competition has almost exclusively been between two companies - Airbus and Boeing.

In recent years, companies from around the world have launched aircraft aimed at breaking the Airbus-Boeing duopoly.

On Wednesday, the latest challenger made its world debut in the form of the Irkut MC-21.

In addition to the Russian Irkut, there are a slew of state-of-the-art airplanes from around the world designed to challenge the Airbus A320neo family and the Boeing 737 MAX-Series.

But before we get to the challengers, lets take a look at the Airbus A320neo and the Boeing 737 MAX.

The Airbus A320neo family of airplanes are updated versions of the company's original A320-family with new-generation engines and optimized aerodynamics.

The line up of medium-range airliners include a trio of models - the 160-seat A319neo, the 189-seat A320neo, and the 240-seat A321neo. All three variants can be equipped with modern CFM LEAP-1A or Pratt & Whitney PW1100G turbofan engines.

Thus far, Airbus has nearly 4,600 orders for the various versions of the A320neo. The first A320neos entered service in early 2016.

Like the A320neo, the 737 MAX is the latest version of Boeing's long-serving short-to-medium range airliner that it has been selling for 50 years.

For MAX duty, Boeing gave its 737 new engines, wings, avionics, and a slew of other updates. The 737 MAX series is made up of four different variants - the 149-seat 737 MAX7, the 189-seat MAX8, the 200-seat MAX200, and the 220-seat MAX9.

The updated 737 is available with new CFM LEAP-1B turbofan engines. Boeing has 3,200 orders for the 737MAX and is expected to enter service in 2017.

Bombardier CSeries

The Bombardier C-Series is Airbus' and Boeing's most prominent rival. Although the Canadian airplane maker has long-been a major player in regional airliners, the C-Series is the first time the company has had to compete against the US and European titans.

The Bombardier airliner has, thus far, struggled to net the level of sales as the 737 and the A320. But the C-Series has garnered critical acclaim for its performance, fuel efficiency, and design.

The C-Series lineup consists of two variants of the plane - the 133-seat CS100 and the 160-seat CS300. In the marketplace, the C-Series competes against the Boeing 737MAX7 and the Airbus A319neo.

Like the A320neo, the C-Series is powered by a version of Pratt & Whitney's revolutionary geared turbofan engines - the PW1500G. The Bombardier C-Series enters commercial service in July and has more than 300 firm orders for the plane.

Embraer E-Jet E2

Like Bombardier, Embraer is also a major regional airliner powerhouse that's moving up to the big leagues to compete against Airbus and Boeing. Embraer's contender is the second generation of the company's E-Jet called the E2. Even though the first generation airplane made a living mostly with regional airlines, Embraer is marketing the the second generation as a smaller alternative to the A319 and the MAX7.

The E2 lineup comprises three variants - the 88-seat E175-E2, the 106-seat E190-E2, and the 132-seat E195-E2.

The E2 is powered by two versions of Pratt & Whitney's geared turbofan engine.

The Embraer E-Jet E2 is expected to enter service in 2018. The Brazilian airplane maker currently has roughly 270 orders for its latest jet.

Mitsubishi MRJ

The Mitsubishi MRJ is Japan's first native commercial airliner in 50 years. The MRJ or Mitsubishi Regional Jet lineup is made up of the 80-seat MRJ70 and the 92-seat MRJ90. Although the MRJ variants are much smaller any of the offerings from Airbus or Boeing, the plane represents a domestic alternative for a country whose airlines have long been one of Boeing's most loyal customers.

The MRJ will also be powered by Pratt & Whitney's geared turbofan engine. The Mitsubishi airliner is expected to enter service in 2018. The company currently has more than 220 orders for the MRJ.

COMAC ARJ21

The COMAC ARJ21 is China's first modern airliner. COMAC or Commercial Aircraft Corporation of China, was founded in 2008 to design and produce indigenous airplanes for the country's burgeoning airline industry.

According to Boeing, Chinese airlines are expected to order more than 6,300 airplanes over the next 20 years with a total value topping $1 trillion.

The ARJ21 is a 90-seat regional airliner designed for short-to-medium range duty. It's powered by a pair of General Electric CF34-10A engines. The Chinese government-owned company currently has almost 350 orders for the plane - mostly from domestic airlines and leasing companies. The ARJ21 entered service late last year.

COMAC C919

The C919 is COMAC's first mainline jet designed to go head-to-head with the A320neo and the 737 MAX. The 168-seat jet is expected to be powered by a pair of CFM LEAP-1C engines.

Thus far, COMAC has 517 orders for the C919 with almost all of them from Chinese operators. The Shanghai-built airliner is expected to make its first flight next year and enter service some time after 2020.

Irkut MC-21

The Irkut MC-21 is the latest airliner to emerge from the Russian aviation industry. The MC-21 will be available in two versions - the 165-seat MC-21-200 and the 211-seat MC-21-300. The MC-21 is available with two engine options - the Russian Aviadvigatel PD14 and the American Pratt & Whitney PW1440G geared turbofan.

Irkut currently has 175 order the MC-21- made almost exclusively by Russian airlines and leasing companies.

Although Irkut does not have a track record in the commercial aviation space, the company and its Yakovlev subsidiary have a long history building some of the world's elite military aircraft.

In addition, Irkut also manufactures components for the rival Airbus A320.

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