Victor Hănescu was the defending champion, but lost in the second round to Florent Serra.
Rui Machado was the defending champion but decided not to participate.
Martin Kližan won the title, defeating Adrian Ungur 3–6, 6–3, 6–0 in the final.
The 2012 Monte-Carlo Rolex Masters was a tennis tournament played at the Monte Carlo Country Club, in Roquebrune-Cap-Martin, France, near Monte Carlo, Monaco. The tournament was part of the 2012 ATP World Tour and was played on outdoor clay courts. Rafael Nadal was the seven-time defending champion of the singles event having won this event in 2011 and successfully defended his title by beating Novak Djokovic 6–3, 6–1 in the final. Nadal's victory was his eighth consecutive Monte-Carlo Masters singles title, having won this event in the past from 2005 to 2011. Nadal became the first man in the open era to win a tournament eight consecutive times.
Novak Djokovic was the defending champion, but lost to Janko Tipsarević in the quarterfinals.
Roger Federer won his record-tying twentieth Masters 1000 title and third title at Madrid by defeating Tomáš Berdych 3–6, 7–5, 7–5 in the final. With this win, Federer overtook Rafael Nadal for the No. 2 ranking.
Benoît Paire chose to not defend his last year's title.
Cedrik-Marcel Stebe was the champion in 2011, but did not qualify for the event in 2012, since he played mostly ATP World Tour tournaments in that season.
Guido Pella defeated Adrian Ungur 6–3, 6–7(4–7), 7–6(7–4) in the final to win the title.
Facundo Bagnis was the defending champion but lost in the quarterfinals.
Adrian Ungur won the Romanian final against Marius Copil 6–4, 7–6(7–3).
Victor Hănescu was the defending champion but decided not to participate.
Andreas Haider-Maurer defeated Rubén Ramírez Hidalgo 6–4, 3–6, 6–4 in the final to take the title.
Mahesh Bhupathi and Michaël Llodra were the defending champions, but Llodra chose not to participate. Bhupathi played alongside Denis Istomin, but they lost in the quarterfinals to Rohan Bopanna and Aisam-ul-Haq Qureshi.
Bopanna and Qureshi went on to win the title, defeating Daniel Nestor and Nenad Zimonjić in the final, 6–4, 6–3.
Lukáš Rosol was the defending champion, but lost in the final to Grigor Dimitrov 7–6(7–2), 6–1
Adrian Ungur was the defending champion, but lost in the second round to Martín Cuevas.
Filip Krajinović won the inaugural tournament by defeating Federico Gaio 2–6, 7–6(7–5), 7–5
Viktor Troicki won the title, beating Louk Sorensen 6–3, 6–2
Julian Reister was the current champions, but chose not to compete this year.
Jaroslav Pospíšil was the defending champion, but lost in the second round to Potito Starace.
Tommy Haas was the defending champion, but could not participate this year due to a shoulder injury.
This was the first edition of the tournament.
Kei Nishikori was the two-time defending champion and successfully defended his title, defeating Kevin Anderson 6–4, 6–4 in the final.
Potito Starace and Adrian Ungur were the defending champions, but Starace did not defend his title while Ungur partnering Victor Vlad Cornea lost in the first round. Victor Crivoi and Petru-Alexandru Luncanu won the title beating Ilija Bozoljac and Dušan Lajović in the final 6–4, 6–3.
Roger Federer was the defending champion, but chose not to participate this year.
