When I had CBT (depression, I managed to dodge PTSD), I was struck by its' parallels with Stoicism, Buddhism and Taoism (I've read a lot of weird stuff). But I'd already seen the similarities between the three classic philosophies. Each of them clearly shows its cultural roots, but all apply a similar approach to life -one which involves the maintenance of personal serenity and detachment from the superficially important concerns of society.

As best I can sum it up, Stoicism rests on these ideas:

Humans are the only creatures that possess the 'Reasoning Faculty'.

This faculty allows us to 'make the proper use of appearances' which means to observe, study and learn from and about the world.

By means of this, we differentiate between 'the things which are in our power, and the things which are not in our power'.

The only things that lie within our power are our own thoughts, atttitudes and behaviours. We cannot control externals (including other people), but we can control how we react to them. It is how we react to a thing that decides whether we are happy and free, or miserable and bound, not the thing itself.

I recommend the Enchiridion (http://classics.mit.edu/Epictetus/epicench.html) and Discourses (http://classics.mit.edu/Epictetus/discourses.html)of Epictetus and the Meditations of Marcus Aurelius (http://classics.mit.edu/Antoninus/meditations.html) , which can be downloaded free of charge from the links provided (as a Yorkshireman, it is physically painful for me to pay for something I can get free).