This is a very difficult question to answer. "All" the major works is a lot! In addition, as you can imagine, Roman religion is a broad topic. For instance, the Romans had religious calendars that guided the seasons and rhythms of life, spatial demarcations of sacred space, public festivals and sacrifices, religious personnel that sought to make sense of the world, direct communication with the gods through fearful prodigies, and even the ability to repair broken relations through expiations.
Here is a short bibliography, which should get you started:
- Valerie M. Warrior. Roman Religion.
- John Scheid. An Introduction to Roman Religion. trans. Janet Lloyd.
- Mary Beard, John North, and Simon Price. Religions of Rome
- Agnes Kirsopp Michels. The Calendar of the Roman Republic
- Eric Orlin. Temples, Religion and Politics in the Roman Republic
- H. H. Scullard. Festivals and Ceremonies of the Roman Republic.
- Bruce MacBain. Prodigy and Expiation.