I’ve yet to encounter a maths book with the winning charm of Alex Bellos’s Alex’s Adventures in Numberland (UK) (Here’s Looking At Euclid in the US). Strongly recommended journey through mathematical ideas, both whimsical and essential.
Speaking of whimsicality, I also recommend Matt Parker’s Things To Make And Do In The Fourth Dimension (UK) (US) and Hannah Fry’s The Mathematics of Love (UK) (US).
A shout out for John Allen Paulos’s Innumeracy (UK) (US) – I fondly remember reading this in the 1990s and having my eyes opened to the world of numeracy and innumeracy.
Jordan Ellenberg’s How Not To Be Wrong (UK) (US) is a story-rich, clear exposition of the maths all around us.
A more unusual pick: Apostolos Doxiadis offers us the rather brilliant mathematical novel Uncle Petros and Goldbach’s Conjecture (UK) (US) which works very well as a novel of obsession and secrecy, but will teach you a bit of maths as a side effect. Doxiadis also wrote the ambitious and excellent Logicomix (UK) (US) – a history of logic in comic form.
Vicky Neale’s Closing the Gap (UK) (US) is an excellent account of recent progress in prime numbers, but also one of the best accounts you’ll read by a mathematician about how mathematics research is done and how it feels to do it.
And recently arrived on my pile, David Acheson’s The Calculus Story (UK) (US) which is a very clear explanation of calculus (wish I’d had it as a maths student!) along with some history of the subject.
My recent book is “Fifty Inventions That Shaped The Modern Economy”. Grab yourself a copy in the US or in the UK (slightly different title) or through your local bookshop.