Odo
Odo is the female philosopher whose thoughts and works serve as a rule, groundwork, for the Utopian life on Anarres. Her philosophy is called Odonianism and it sums up to the way of life where people are free from the pressures of laws and possessions, everyone is equal and everyone is free to choose to contribute to the society however they want.
Both planets a moon to each other
Urras and Anarres are often times in the novel said to be moons to one another. People on both planets are looking at their moon secretly wondering about the life there. This sort of wondering encourages Shevek to want to take down the walls and bring the worlds together
Time
Time is the most obvious motif of the novel. The novel itself is structured to agree with Shevek's temporal theory that time moves in a cycle. The novel begins with him leaving Anarres and it circles back to the end where he is traveling back to Anarres.
Walls
There is an off mention of the walls, particularly walls that Shevek wants to take down. These walls are walls of actual isolation of Anarres and the isolating nature of the mindset on Anarres where people, despite being taught of living in freedom, are more than ready to isolate those who think differently from what is custom.