The major value system shown is based on the importance of friendship. Throughout the book, the main characters act in selfless ways, showing how their friendship overcomes obstacles such as greed and violence. Water Rat is a good example of this; he is always kind and helpful to his friends, even the initially loathsome Toad. Rat is even friendly to the hostile stoats and foxes in the woods, although he keeps a cautious eye. Near the beginning of the book, Mole, who is overcome with the joy and beauty of the above-ground world, tries to row Rat's boat, and ends up tipping it over. Rat saves him from drowning, and Mole is mortified, but Rat waves it off:

"That's all right, bless you!" responded the Rat cheerily. "What's a little wet to a Water Rat? I'm more in the water than out of it most days. Don't you think any more about it; and, look here! I really think you had better come and stop with me for a little time... And I'll teach you to row, and to swim, and you'll soon be as handy on the water as any of us."
(Grahame, The Wind in the Willows, gutenberg.org)

Rat's love of friendship allows him to overlook even Toad's excesses of character; although he does lose his temper at times, he is always willing to forgive and forget. The themes of friendship extend throughout; each character supports the others in their times of need, although Toad sometimes needs to be prodded, and Badger is anti-social but very willing to help when Rat and Mole are caught in a snowstorm. Overall, the values of friendship and selflessness are prevalent in the main characters and in the themes of the story itself.