The book gives a detailed introduction to the NTRU cryptosystem and its attacks. First we give some mathematical background where we consider the ring on which NTRU is based on and we introduce some important properties of this ring. Then we introduce the cryptosystem where we see two possible ways to decrypt. Followed by this we do a security analysis where we introduce the most important attacks against NTRU. The most interesting attacks are the lattice attacks where we spend a whole chapter to these sorts of attacks.