For motor manufacturers, concept cars can mean a great deal, or they can mean nothing at all. Often, they're a way of gauging public interest before committing to production. But all too often, they're 'celebratory' models, or indications of future design intent. In some cases, some manufacturers seemingly build concepts merely to disappoint us by never actually producing anything vaguely reminiscent. So with that said, here are ten concept cars we thought should've reached production, but never did, and likely never will.

1. 2006 Lamborghini Miura Concept

The Lamborghini Miura is widely regarded as one of the most beautiful supercars ever. In 2006, Lamborghini celebrated the 40th anniversary of the original Miura concept with the gorgeous green concept you see here, penned by then chief of design, Walter de Silva. Technical details were kept a secret, but there was never even a hope of it reaching production. Then CEO of Lamborghini, Stephan Winkelmann said, "The Miura was a celebration of our history, but Lamborghini is about the future. Retro design is not what we are here for. So we won't do the Miura."

2. 2010 Audi Quattro Concept

What better way for Audi to capitalize on its rich heritage in motorsport, and particularly in the World Rally Championship, than to build a modern version of the infamous Quattro rally car? Well in 2010 Audi teased us with just that. To celebrate 30 years of quattro all-wheel drive, Audi unveiled the sleek two-door Quattro Concept in Paris. It was based on a shortened RS5 platform, weighed in at a measly 2,866 pounds, and kept to the Ur Quattro's ethos by packing the same 2.5-liter unit from the RS3, but dialed up to 403 horsepower. It would've been an exceptional celebration of Audi's AWD-prowess, but it never reached production.

3. 2009 Bugatti 16C Galibier

After the Bugatti nameplate was revived by Volkswagen, resulting in the rulebook-rewriting Veyron, everybody wondered "what next?" for Bugatti. The 16C Galibier was a hint at what could've been. It was characterized by a central rib that ran the length of the body – a throwback to the Bugatti Type 57SC Atlantic – and was met with great interest when it debuted in Frankfurt in 2009. Powered by an 8.0-liter twin-supercharged W16 engine – derived from but not the same as the unit in the Veyron – it produced in excess of 1000 hp, and could manage a top speed of more than 235 mph.

4. 2014 Infiniti Q50 Eau Rouge

When the now Cadillac president, Johan de Nysschen, was at the helm of Infiniti, he envisioned a rival to the BMW M3 and Mercedes-Benz C63 AMG. In 2014, Infiniti revealed the Q50 Eau Rouge concept. The super-sedan was named after the sweeping left-hander at the Spa-Francorchamps circuit in Belgium and was much more than just a static design concept. No, the Q50 Eau Rouge packed the Nissan GT-R's 3.8-liter twin-turbo V6 under the hood, developing 560 hp and 443 lb-ft of torque. It was mated to an all-wheel drive system – though not the same one as the GT-R – and looked to be the M3's worst nightmare.

5. 2008 BMW M1 Homage Concept

BMW has a rich history, filled with great racers and segment-defining street cars. But amongst generations of series models, the original BMW M1 supercar is still a holy machine amongst enthusiasts. In 2008, BMW honored the original with a truly fitting concept – commemorating 30 years since the release of the original. It too was a rear-mid engined supercar, penned by Giorgetto Giugiaro who designed the original, and it wore a similarly striking orange color and the dual BMW logos on the rear. But BMW never intended on taking it to production – it was merely to honor a hero of the past.

6. 2014 Hyundai PassoCorto

We're still getting to grips with the idea of Hyundai as a performance brand - its new Veloster N giving us a first look at its ability to produce a proper hot-hatch. But back in 2014, Hyundai showed strong intent when it released the PassoCorto concept. The striking sports car was a compact 2-seater - its name translating literally as 'short wheelbase' - that was the product of a design competition hosted in partnership with Hyundai and the Istituto Europeo di Design of Turin. The PassoCorto proposed using a mid-mounted 1.6-liter turbocharged inline-4 to drive the rear wheels of what could've been an Alfa Romeo 4C-fighter.

7. 2014 Mini Superleggera Vision Concept

In 2014 at the Concorso d'Eleganza Villa d'Este, the open top collaboration between Mini and Touring Superleggera – called the Mini Superleggera – was revealed. It melded contemporary design elements with traditional Mini 'Britishness' in a striking package that would've been incredible in production guise. The Mini Superleggera had an eye on the future though, as it was powered by an electric motor. It never made it to production – but just imagine what Mini could've become if it had made it.

8. 2010 Jaguar C-X75

Remember the Jaguar XJ220 hypercar of the 1990s? Few do, but when it was around it actually set the record for the world's fastest car – a record only beaten by the McLaren F1. In 2010 Jaguar sought to reinvent the XJ220, but suitable for the future. An archaic combustion engine would be out of the question, so the all-electric C-X75 was born. Its four electric motors produced 778 hp, and the batteries were to be charged on the go by two diesel-fed micro-gas turbines. There were plans to produce the C-X75, albeit as a hybrid with a turbo-gasoline motor, but they never materialized due to the ongoing global economic crisis getting in the way.

9. 2013 Nissan IDx

Nismo Small cars are fun – add in rear wheel drive and retro styling, and you've got a winning formula. In 2013, Nissan unveiled twin IDx concept cars to the world – styled to be reminiscent of the old Datsun SSS. The IDx Nismo was the one that caught everybody's attention though – with a racy livery, boxy flared styling, and the promise of a compact, lightweight rival to the Toyota 86, with a boosted 1.6-liter engine at its heart. The attention garnered by the IDx Nismo concept was massive – and Nissan constantly flirted with the idea of production, refusing to rule it out. But we're now 5 years down the line and it still hasn't materialized.

10. 2015 BMW 3.0 CSL Hommage R

Another BMW Hommage concept, but one deserving of a place on this list; built to commemorate the original 3.0 CSL 'Batmobile,' the 3.0 CSL Hommage R debuted at the 2015 edition of the Concorso d'Eleganza Villa d'Este. It was built with a lightweight racing inspired interior, and was powered by an inline six-cylinder engine complete with an eBoost hybrid system. It utilized liberal amounts of aluminum and carbon fiber, but like the M1 Homage and the 2002 Hommage, it was a celebration of the past, not an indication of the future.