Lysimachus, son of Aristides, and Melesias, son of Thucydides (not the historian Thucydides), request advice from Laches and Nicias on whether or not they should have their sons (who are named after their famous grandfathers) trained to fight in armor. After each gives their opinion, Nicias for and Laches against, they seek Socrates for counsel.
Socrates questions what the initial purpose of the training is meant to instill in the children. Once they determine that the purpose is to instill virtue, and more specifically courage, Socrates discusses with Laches and Nicias what exactly courage is. The bulk of the dialogue is then the three men (Laches, Nicias and Socrates) debating various definitions of courage.
Nicias argues in favor of an education in fighting in armour for young men. He mentions that it promotes physical fitness, prepares a man for military duties, gives an advantage over untrained opponents, helps one understand military strategy, makes one braver, and gives one a martial appearance.
Laches argues against the need for fighting in armour by claiming that the Spartans do not practice it; the instructors that Laches has seen are not brave soldiers and so have not benefitted from this knowledge; and it causes cowards to take foolish and damaging military risks.
Melesias and Lysimachus ask Socrates to decide which side is correct. Socrates begins by trying to clarify what the actual topic is. He determines that the issue is the care of young men's character and asks if there are qualified teachers for this. Socrates confesses not to be skilled in this and assumes that Laches and Nicias are either versed in character building or else know of experts in that field. Socrates proposes to question them about this to see if they have qualified expertise.