According to the official page for High School DxD, the third season will be airing in April of 2015. The show itself, which is based off of the light novel of the same name began in 2008 Fujimi Shobo’s Dragon Magazine(1). The anime originally aired back in January of 2012. The website also released a key visual (pictured below) for the next season list

Here is a brief plot synopsis for the show for those who have not seen it:

Kuoh Academy is a former all-girls school that has recently turned co-ed, but it has a secret. Unknown to normal humans, angels, fallen angels and devils comprise part of the student population. One of these students, Issei Hyodo, is a lecherous second-year human student who lives a peaceful life. After an ordinary school day, Issei is suddenly asked out on a date by a girl named Yuma Amano. After their date, Yuma brings Issei to a local park and makes a startling request. She reveals herself as Raynare, a fallen angel, and she tries to kill him. Using his summoning card, Rias Gremory, a buxom third-year student at Kuoh Academy, revives him. Issei wakes up the next morning, thinking that the events that occurred were all just a dream. Immediately after being attacked by another fallen angel and waking up, he notices Rias naked in his room. Rias reveals to Issei her true identity as a devil and says that as a result of his death at the hands of Yuma, she has reincarnated him as a devil, becoming his new master in the process. From Wikipedia

So fans of the show, get excited for the wait is slowly coming to a close and at the very least, it is in sight.