Princes of the Renaissance first appeared from Wallace's own Warfrog Games in 2003, and like many Warfrog releases, the game had a single print run, then vanished from the market. Mercury Games has obtained worldwide rights to the design, and notes that it "has further refined the game with gameplay improvements, new tiles, and other items sure to appeal to fans of the game or those who will get to experience the Wallace-classic for the first time".
Details of those "improvements, new tiles", et al. will be released by Mercury at a later time. In a press release announcing this new edition, Richard Diosi of Mercury Games said, "We know how important it is to treat the product with the respect it deserves, while ensuring that the game benefits from the many thousands of plays over the past few years."
For those not familiar with the design, here's an overview: