There is no scientific evidence for life after death, but the belief in an afterlife is strong among religious and also some non-religious people.
For most religious people, belief in life after death is based on teachings in their scriptures or traditions. The sacred texts in Christianity, Judaism and Islam talk of an afterlife, so for followers of these faiths life after death has been promised by God. For Buddhists, belief in reincarnation is based on the tradition that the Buddha remembered his past lives when he reached enlightenment.
Not all people who believe in life after death would call themselves 'religious'. For example, some people believe in the concept of reincarnation but are not necessarily Buddhist, Hindu or Sikh. Others feel natural justice requires good to be rewarded and evil punished but do not hold one of the traditional faiths that promise an afterlife.