The Sumerian faith is a polytheistic one centred around the active influence of the gods on human civilisation and life on Earth. It holds that civilisation is a gift from the gods, and that we are intended to use this gift to uphold the principles of cosmic order as laid out by the gods at the creation of the world. These principles include justice and order, but also fairness and equity. Greed, tyranny, and intolerance are unacceptable in the eyes of the gods, and retribution would fall upon a ruler who brought oppression to their people, or on a person who sought to accumulate wealth without care for their fellow human beings.
The relationship between humans and deities in Sumerian faith is not one of equals. It is recognised that the gods occupy a higher position than humans. A social contract exists between humans and gods, in which the gods provide all of the things necessary for people and civilisations to thrive. Humanity, in turn, should work to ensure that our societies are fair and equitable, and we should serve and worship the gods in recognition of these gifts.
Mesopotamian deities were depicted in anthropomorphic form, radiating a divine power called 𒈨𒉈 melam. This power may be roughly understood as "awe-inspiring splendour", provoking a wondrous, fearsome, all-encompassing feeling of awestruck veneration and wonder in humans presented with it. (It was also not unique to deities, as it could be worn by kings and heroes, as well as demons, and even cities.)
The deities of ancient Mesopotamia number in their thousands, with different deities being revered at different times by different cities and empires. A common exercise for scribes in training was to copy lengthy lists of deities, so we know many of their names, if not the function of their worship in every case. These deities had a complex web of familial and syncretic relations, with influences from all the cultures that lived in Mesopotamia colouring the religious landscape of the region.
The deities form a hierarchy, although the precise composition of this hierarchy varied over time. At the top were the "seven who decree Fate", seven who held the ultimate authority over destiny. Then came an assembly of "great gods", who may be identified with the term 𒀀𒉣𒈾𒆤 anunaki, although the precise implications of this term varied over time. There were countless further minor deities, many of whom little is known about save for a name.
The gods desire a personal relationship with their followers. Despite the huge number of deities attested in Mesopotamian history, people generally wouldn't worship the entire pantheon, but would have personal and civic deities, by whom they or their cities were called. As with many religious traditions, prayer is a way to build up a relationship with the gods, and more on prayer in Sumerian tradition can be found on this site's article on prayer. If you are experiencing a connection with a Mesopotamian deity and want to know how best to approach them, this is a good start.
Strengthening this relationship calls for worship and devotion. In ancient times, temples were focal points of major cities, and the statues of the gods, in which the gods themselves were believed to dwell, were cleaned, fed, and attended by temple staff. In modern terms, this is obviously impractical, and it is necessary to practice our faith in a way that is consistent with the principles of modern society and the resources available to us.. An article elaborating on worship in modern times can be found here.
A lot of devotional work in Sumerian tradition is done at an altar. Those who are serious about pursuing a relationship with the gods in the modern age should endeavour to construct one in a room in their home. More information can be found on this site's articles about building an altar, and making offerings.
Sumerians believed that the physical world was a mirror of the spiritual in many ways, and this concept plays an important role in much of Sumerian cosmology. Society, as instituted on the Earth by the gods, was meant to be a reflection of how divine society was laid out. Statues of gods are taken to hold the very real presence of the god within them, and should be treated in the same way as the god themselves.
Another important concept is that of 𒈨 me (Akkadian: paršu). Enlil, the father of the gods, created the me at his temple E-kur, and gave them to the wise god Enki to distribute to the cities of Sumer. These are the gifts of civilisation; the principles of technology, writing, truth, beauty, justice, and order that enable civilisation to exist. They are part of human experience, for better or worse, and underpin the Sumerian concept of morality, which we look at on our page on good and evil.
They are described as physical objects, and gods could transfer them from one location to another. The Sumerians understood this to be a way in which domains, powers, and attributes could be transferred between, or won by, deities. Inana, in particular, is told in a number of texts to have schemed or conquered domains from other deities.
The Sumerian conception of the underworld has been much maligned and misrepresented on the internet and in other pagan spaces. It wasn't necessarily a dreary grey wasteland. Find out more in our article on death and the afterlife.