Although established as the current standard in catheter ablation, radiofrequency energy has significant limitations. To produce a continuous line of conduction block, radiofrequency energy requires contact between the electrode and endocardium throughout and produces a lesion limited in depth and prone to endocardial disruption. As the predominant case mix of catheter ablation shifts from supraventricular tachycardias towards atrial fibrillation and ventricular tachycardia, interest has grown in alternative energy sources. Cryothermy offers the advantages of low risk of endocardial disruption and thrombus formation with extensive previous surgical experience in the treatment of cardiac arrhythmias. Ultrasound and microwave have the advantages of being contact forgiving and having excellent depth of penetration without an apparent higher risk of endocardial disruption than radiofrequency. Diode laser produces controlled low energy ablation and can be delivered through a range of optical fiber configurations including loops and balloons to produce thin continuous lesions. The use of optical fibers for laser delivery also provides an option for reflectance spectroscopy as a feedback mechanism on both contact as well as lesion progression in real time. Each of the above energy sources have potential clinical advantages in epicardial as well as endocardial ablation.