Efficiently Inefficient is a semi-technical survey of buyside finance, explaining how different strategies (e.g long/short equity, quant equity, macro, credit, arbitrage) work, accompanied by interviews with leading practitioners (e.g Ken Griffin, Cliff Asness, John Paulson).

Some of my favourite ideas in the book:

• Efficient Inefficiency: markets are just about inefficient enough to compensate traders for the act of trying to make markets more efficient. As a corollary, we would expect most strategies (credit, equity, macro) to average out to approx the same returns over time.
• Backtest-regression equivalence. Predictive regressions are mathematically equivalent to backtests!
• Heisenberg uncertainty in finance: executing trades obeys an uncertainty principle, where you cannot arbitrarily get precise execution time and market impact. e.g if you decide that you need to execute in some short time window, you have to allow for a big market impact.
• Expectations hypothesis: in theory, the shape of the futures curve embeds expectations for spot moves. In reality, you can earn some risk premium for being long spot when the curve is in contango.
• Soros boom-bust cycles: every bubble requires a real trend, a misconception of the trend, and a feedback loop that links the two

But the big problem is that Pedersen hasn't decided what level of abstraction to pitch the book at. It's technical and is written in a rather academic way, with a focus on the academic literature more than practical results. The interviews are nowhere near as valuable as those in Market Wizards or Inside the House of Money. As a result, I'm not sure who to recommend this to.