NPD Bookscan has reported 2018 print sales at 707.4 million, the highest since 2010.

Michelle Obama’s Becoming played a big role in that, and of course in previous years it’s been JK Rowling. Nice to know, in this era of diversity in publishing, that women authors are keeping the industry afloat.
Over at Publishers Lunch Michael Cader explains more:

Michelle Obama’s BECOMING pulled the market, selling approximately 712,000 tracked copies in the last full pre-Christmas week, and adding another 243,000 copies in the final sales week of the year (which included December 23 and 24), registering total hardcover sales of 3.428 million copies. Dav Pilkey’s newest Dog Man book published December 24 and sold tracked copies of 182,000 units in the final sales week.
…Adult nonfiction comprised 296.6 million units overall, in keeping with the trend of recent years, while adult fiction appears to have been modestly soft. Though backlist gains led the market in the recent years, thanks to Michelle Obama’s hit memoir, frontlist sales look to have been slightly positive for 2018, at 266 million units overall.

That’s just for tracked print, where NPD Bookscan will be covering pretty much all sales.
Cader notes that,

PubTrack Digital ebook data, available through August 2018 only so far, had ebook unit sales declining approximately 7.6 million units, so it’s not clear yet whether total monitored book sales for the year will up slightly, flat, or down slightly.

Audiobook sales again need to be accounted for, but as Cader notes,

There is no good data source to reflect the growth in digital audio sales units.

That’s an intriguing comment to end on.
On the one hand Publishers Marketplace, which publishes Publishers Lunch, offers paid access to Bookscan’s comprehensive print book sales data so the observation might be deemed biased.
But the only other party claiming to have a handle on the sales and revenue from ebooks and digital audio is Data Guy of Author Earnings and BookStat fame, who has been noticeably absent from the ebook debate this past year.
It is almost a year to the day since the January 2018 Author Earnings Report divulged selected statistics from the $10 million paywall BookStat to tell us how many books, ebooks and audiobooks were supposedly sold in 2017.
Supposedly? TNPS has taken a look at those numbers and they just don’t add up.

Ebook sales doubled in US in 2018 according to Data Guy’s nonsensical BookStat numbers

Data Guy rewrites the historical Author Earnings US ebook statistics. 2016 US unit ebook sales of 487 million now 525 million. What are we to believe?

The report evoked considerable controversy and since then Data Guy has kept a low profile, with one appearance at the SFWA Nebula Conference and one at Digital Book World 2018 where he studiously avoided offering us any useful data about the book markets
Will we see another Author Earnings Report this year? Only Data Guy knows the answer to that, but it’s looking unlikely.
In responses to comments in January Data Guy promises that there would be one in a few months, incorporating some suggestions from readers.
A year on and there has been no further Author Earnings Reports, just slideshows stuck on the site from the SWFA and DBW events. Data Guy hasn’t even bothered to respond to comments on those.
So it looks like we’re stuck with such data as Nielsen and others offer us, which may be for the best.