The Dutch at the time were the leading trading nation in the world, rich and becoming richer, and were busy inventing most of modern banking in order to manage that wealth. Tulip mania was a bubble market in tulip bulbs, fueled by the invention of futures and options contracts, and at its peak [a contract for future delivery of] a single rare bulb might cost as much as a house. It was made famous by the account in Charles Mackay's "Extraordinary Popular Delusions and the Madness of Crowds", one of my favourite books, although Mackay sensationalized the story to a great extent.
Tulips take a decade or more to be grown from seed to flower - so breeding a new variety is a long process with uncertain outcomes - but grow in a single season from a bulb, and can be propagated from nodes which form on the bulbs, allowing an existing variety to be reproduced. They are also susceptible to viral infection which causes petals to grow in different patterns and shapes, yielding a huge variation in forms including extreme rarities. They were also quite novel at the time - they had only been cultivated in Europe for a few decades - and represented Dutch success, ingenuity, and care. The combination of these factors, with the wealth that was sloshing around at the time, made for a natural bubble. The bubble formed in mid-1636, after the bulbs for that season were lifted and could be readily traded. In September/October, the bulbs should be back in the ground in order to flower the following spring, and so the trade shifted from physical bulbs changing hands to futures contracts and then to newly-invented derivatives. That took the brakes off and prices shot up swiftly, until the crash in February.
Unfortunately Moggach ignores most of this splendid history for plot reasons (for instance, her bubble is already well-established at the start of 1636, and a late plot twist depends on a single bulb physically changing hands in mid-November). More seriously, the central romance in the novel is between two deeply unlikeable people - short-sighted, vain, selfish, deceptive, feckless - engaged in a vile scheme. When Jan neglects his student, I want the student's father - a butcher - to come around with the tools of his trade and exact bloody vengeance. When Sophia stands on a bridge and contemplates suicide, I long to push her in.
There's much to like about the book: rich descriptive prose, a vividly-realised and plausible society, a charming secondary romance between the two most likeable characters (which is almost fatally destroyed by the feckless central couple), some interesting reflections on the nature and pace of individual change. There's also quite a bit of art history - which may or may not be any more accurate than the economic history - together with a number of plates in my edition. But overall I'm disappointed.