This is Plato's best known work and is also considered his most influential especially when it comes to the fields of philosophy and political theory. The Republic is divided into ten books and in each book Socrates discusses different topics from the immortality of the soul to the meaning of justice with his disciples like Glaucon, Thrasymachus, Adeimantus and others.
The first two books focus on justice and its meaning. After hearing the arguments of his disciples, Socrates made a very enlightening statement when he said that it's the advantage of a person to be just and it's his disadvantage to be unjust. A statement like this can be very much true today as it is thousands of years ago. After that, they continued their discussions about education and the guardian class. I'm sure many have already heard about the guardians, in this book Socrates referred to them as the ideal rulers of an ideal city.
Book eight of the The Republic discusses the different types of government, some of which we're familiar with today. Socrates referred to the different types of governments as timocracy, oligarchy, democracy and tyranny. It's interesting to note that he considered these types of governments including democracy as unjust. He said that in a democracy there's a strong tendency for the poor people to revolt against the rich class because the rich enjoy too much freedom in this kind of government.
This work by Plato is a timeless classic and it laid the ground work for many important modern philosophical and political ideas. This book is definitely a good read especially to political science or law students and the philosopher in all of us.