Football, much like any professional sport, is one which is very often governed by the laws of rivalry. Some are casual altercations that simmer in the match-day heat before dissipating from the public conciousness once the full-time whistle is blown - but there are more than a handful of big derby day clashes that no amount of silverware can ever replace, no managerial changes can eradicate and not even time can change. These are the big moments in the club football calendar that remain with us long after the match ends and continue to make us excited year after year.
Whether its local pride, the battle to prove oneself against a noisy neighbour or the chance to avenge past defeats, these fixtures always get their respective players riled up. Often times, clubs will save their best performance of the season just for matches like these - because to lose would mean shame and regret for weeks and months to come.
Ranging from Ireland to Argentina, there are a whole host of magnificent games where fierce competitors go head-to-head in an effort to prove themselves, but for this particular selection only matches from a country's top league have been considered. This list focuses largely on European battles due to the number of high-quality derbies situated there, but a select few from elsewhere have also been included. Notable absentees include the North London derby and the Tyne-Wear derby, excluded to avoid too much emphasis on one country; after all this list intends to focus on the best world football has to offer, as much as possible.
Nevertheless, there is something here for just about every type of football fan, whether you're a follower of the Irish Premier Division, La Liga, the Premier League, Dutch Eredivisie or the Campeonato Brasileiro Serie A.
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15 Dublin Derby: Bohemian vs. Shamrock Rovers
This Irish Premier Division clash is over a century in existence and it's no stranger to its fair share of brow-raising incidents and crudeness. Grabbing headlines a number of years ago when a severed pig's head was thrown on to the field of play before kick-off, it is also partial to violent scuffles between both sets of supporters.
Shamrock Rovers are Ireland's most successful club having captured 17 league titles, while the Bohemians are a good bit behind them with 11 - but the rivalry stems more from a natural north-south divide created by the River Liffey than it does from silverware. Most recently, back in March, a crowd of over 4,000 turned out to watch - a particularly large number for an Irish football match that underlines how important it is to the loyal fans.
14 Intercontinental Derby: Fenerbahce vs. Galatasaray
Renowned for its lively atmosphere and often grotesque violence, it often gets neglected due to the lack of big name players in the Turkish domestic game. Nevertheless, it is never far from the headlines and is often mired in controversy.
In recent times, the long-standing rivalry has seen itself boil over to appalling levels when a Fenerbahce fan was tragically stabbed to death by a pair of Galatasaray supporters after the Istanbul derby in 2013. On a lighter note, back in 1996 Graeme Souness enraged the Fener fans by cheekily planting a gigantic yellow and red flag in the middle of the pitch after a huge cup final win - a gesture that has seen him become a club legend.
13 Le Classique: Paris Saint-Germain vs. Olympique Marseille
The biggest club fixture in France has pitted so many ideals against each other since it began, and it's always adding new ones. In recent times it has not only been a clash of capital-south or new-old, rather it has become a clash of differing styles and, most importantly, a top-of-the-table wrestle for the Ligue 1 crown.
Skirmishes between the fans are common. The most recent title decider saw as many as eight Marseille fans taken into custody after a fight broke out outside the Stade Velodrome in April. Thankfully, the on-pitch battles are equally as entertaining - their recent 3-2 cracker evidence to that, a match that played host to a number of exquisite goals, none less so than Blaise Matuidi's long-range wonder-strike.
12 Derby Della Madonnina: AC Milan vs. Inter Milan
The first of two Italian derbies on our list, this one makes the cut despite how little it has mattered in deciding the Serie A in recent years. Two waning forces in the game, neither side have replicated their form of old in recent seasons, despite holding 36 league titles between them.
Some of the sport's top players have featured in this historically entertaining battle such as Ricardo Kaka, Paolo Maldini, Marco Van Basten, Javier Zanetti and many more. Struggling to break into the Champions League places, neither outfit has been able to keep pace with Juventus, Roma or Lazio - but until they do so, they will use the Milan derby as motivation to succeed in the long-term.
11 De Klassieker: Ajax vs. Feyenoord
It's interesting to note that Ajax have won twice as many Eredivisie titles as their fierce adversaries and they have also emerged victorious in four of the last five De Klassieker meetings - something that has only served to propel De Stadionclub to chase after De Godenzonen with added haste.
Ajax certainly have a more lavish history, featuring some of the best players to ever play the game such as Johan Cruyff, Marco Van Basten and Luis Suarez. Feyenoord, too, have attracted great players - but it's not always for the football that this match is remembered as the disgustingly violent Battle of Beverwijk clearly attests to.
10 North-West Derby: Manchester United vs. Liverpool
A rivalry borne out of a battle for silverware throughout the early 90s and 2000s, this is unlike many of the other derbies featured on our list. Throughout much of this season, with both teams going through somewhat of a transitional period, it has been less about silverware and more about securing their places in a certain prestigious European club competition.
Right now, the bragging rights are with the Red Devils who defeated Brendan Rodgers's men 2-1 at Anfield in March. However, it's the Reds who have a better chance of securing silverware this season as they remain in the FA Cup. Although they might not be in direct competition as much as they were, the fans still love to lord it over each other when things go their way.
9 Derby Paulista: Palmeiras vs. Corinthians
Two of the most successful clubs in Brazilian football history, this match has long been considered the most mercurial of rivalries. In short, it is extremely volatile, competitive and strained - and there has always been a tangible hatred between both clubs ever since Palmeiras were first formed by a breakaway group of Italian players from Corinthians as far back as 1914.
Epitomising just how far removed certain matches can be from the usually eye-catching skill and flair of Brazilian football, there has been more than one occasion were tensions have ran amok with rioting, brawls on the pitch and nasty challenges. Because although Brazil is often credited as being the spiritual home of the beautiful game they don't half know how to turn it nasty.
8 Manchester Derby: United vs. City
"On derby day in Manchester, the city is cut in two. The Blues and the Reds invade the streets, and if your team wins, the city belongs to you." Those are the purposefully poetic words of Eric Cantona - his quote reveals a great deal about just how intrinsic the result is to both teams.
A notoriously difficult match to predict and doubly taxing to play in, it's been a feisty encounter all 169 times - and United's recent 4-2 win was certainly no exception. Champions of England 24 times between them, there has been an extra amount of pressure riding on it in recent years ever since the Citizens received a huge injection of cash and Sir Alex Ferguson departed Old Trafford.
7 Merseyside Derby: Liverpool vs. Everton
Another battle in England, Merseyside plays host to one of the most heated derbies in world football between Liverpool and Everton. Liverpool have been the most prolific side of late, achieving a much better placing in the league on a more frequent basis.
The Toffees have failed to beat the Reds since 2010 in the Premier League, and although the last meeting ended in a draw with five yellow cards, it's interesting to note that as many as 26 red cards have been shown in meetings between the two sides; always a match that stokes the emotions and raises the temperature.
6 Old Firm Derby: Celtic vs. Rangers
The Old Firm derby has not been allowed to shine as brightly in recent years, but with over 400 meetings behind them, there really is a great deal of history there. With Rangers consigned to the Scottish Championship, the match-day allure of their normally riveting battle has been greatly reduced.
In danger of totally losing its appeal, some fans have gone out of their way to prove that the infamous derby no longer exists, citing Rangers' recent dissolution as proof. That said, watching their last meeting early in 2015, it was plain to see just how much it still means to both sets of fans and players - particularly fiery Celtic captain Scott Browne.
5 Derby Della Capitale: AS Roma vs. Lazio
A truly inflammatory clash, this sees insiders and perceived outsiders go to blows time and again in Italy's most explosive tie. Most recently, in the Serie A, the closely-contested encounter ended in a 2-2 draw as goals from Stefano Mauri and Felipe Anderson were cancelled out by a delightful brace by one-club hero Francesco Totti.
Not averse to some violence, they have often been spoiled by outrageous vehemence from some fans. Back in 1979, one Lazio fan was tragically killed by an emergency flare fired by Romas ultras. Back on the pitch, their overly-zealous relationship is heightened further by the fact they begrudgingly share a stadium - but one thing they share more readily than that is the eternal competition in the Eternal City, something that fuels their battles no end.
4 Der Klassiker: Bayern Munich vs. Borussia Dortmund
With their upcoming German Cup semi-final set for the end of April 2015, the hype is already starting to flow freely. The draw of this match remains very much intact despite Dortmund's spectacularly sudden implosion under Jurgen Klopp. Floundering spectacularly, Die Schwarzgelben have not cut a hugely imposing figure and yet the anticipation has stayed.
From kick-happy goalkeepers and jersey-swapping stars, this is a match-up riddled with a subtext of anger and betrayal, and it's constantly being topped up.
3 Madrid Derby: Atletico vs. Real
Two of Spain's greatest clubs, they have had a very long and distasteful relationship often fuelled by a misconception about exactly why fascist dictator General Franco was so much more fond of Los Blancos than he was of Atleti; in truth, he was merely using Alfredo di Stefano's five-time European Cup winning displays as propaganda for his own regime.
Still, to this day, groups of ultras such as the Frente Atletico and the Ultras Sur use this period in history to mock and enrage their opponents, but most tune-in purely for the fantastic football on display - something that even saw them contest the Champions League final back in May, 2014.
2 The Superclasico: River Plate vs. Boca Juniors
When River Plate face Boca Juniors in the Superclasico, they get pulses racing - and they have been doing so for over 100 years as the first-ever derby between the pair took place in August, 1913. Since then, they have gone on to become the most successful Argentine clubs.
Whether it's in Estadio Monumental or La Bombonera, there is rarely a shortage of talking points when tempers flare and talent rises to the top. A clash that epitomises the cultural and societal divide, it brings out the best of some of the most supremely talented players that has seen Ariel Ortega, Alfredo Di Stefano, Juan Roman Riquelme and Diego Maradona all exude brilliance on the field of play.
1 El Clasico: Barcelona vs. Real Madrid
The footballing world stands still when these two sides square up. Because while local derbies mean so much to so many die-hard, dedicated fans, this one transcends boundaries like no other. Back in late 2014, nearly 500 million spectators tuned in to watch - evidence that it remains the biggest derby in world football by a country mile.
A constant source of anticipation, colour and exuberance, it is a must-watch for football fans everywhere. With Lionel Messi and Cristiano Ronaldo both the leading lights of their respective teams, scoring goals for fun, the reasons for watching are truly endless. In truth, only the most supremely talented players feature in this one and it never fails to amaze.