"Selection for the Lions is the pinnacle of any rugby player's career, and I am so happy to be going," said Bath prop Stevens.
"It has been a whirlwind season for me to date. To go from England A squad involvement to full England selection and now this is incredible.
"It will take some sinking in."
Meanwhile, Saracens star Richard Hill, who has only just started his comeback following long-term injury problems, is thrilled to have the opportunity of a third Lions tour.
"It is always a great honour to be selected for the Lions, but I appreciate that there is still a lot of hard work ahead of me," said Hill.
"I've got to get a lot of match fitness under my belt."