Like someone else’s kid that you only see once in awhile, Amazon’s ebook library is shockingly larger every time you look at it. As of this writing, there are now 151,636 titles in the list of ebooks in Amazon’s Kindle Owners’ Lending Library.

Amazon’s library was born on November 3, 2011 and was the runt of the ebook library litter with only around 5,000 ebooks in it. At the time, most ebook libraries had far more titles that that in their collections. But the Kindle Owners’ Lending Library had good genes and a strong appetite.

Amazon fed their baby well and in just 96 days, the library had grown to contain over 100,000 ebooks. It dwarfed all the other ebook libraries before it was even one month old. The New York Public Library and its 26,466 ebooks looks like a baby compared to the Kindle Owners’ Lending Library.

But just like all babies as they get bigger, Amazon’s library appears to be growing a little bit slower as it ages. A little over 50,000 ebooks were added in the 95 days since the library cracked 100,000 titles. Almost 500 ebooks added a day is still very impressive, but it is definitely slower than the 1,000 ebooks that Amazon was adding a day before it hit 100,000 titles.

One reason for the slower growth rate is that Amazon appears to be a lot more concerned about the quality of ebooks that it lets into its lending library. Amazon actually crossed the 150,000 ebooks mark last Thursday, but if you checked the library on Sunday there were less than 150,000 titles. They had trimmed some of the ebooks between Thursday and Sunday of last week. This definitely shows that they are filtering out titles periodically from the library.

Another example of this quest for quality is the recent addition of the Harry Potter ebook series to the Kindle Owners’ Lending Library. Amazon claims multiple current and former New York Times Bestsellers in the program, but the Harry Potter deal brings the most popular book series ever into the library.

The Kindle Owners’ Lending Library is barely six months old and it already has more ebooks that many popular public libraries combined. We can only imagine what it will look like once it’s all grown up.