Is there an Amazon.com API to retrieve product reviews?

Update 2:

Please see @jpillora's comment. It's probably the most relevant regarding Update 1.

I just tried out the Product Advertising API (as of 2014-09-17), it seems that this API only returns a URL pointing to an iframe containing just the reviews. I guess you'd have to screen scrape - though I imagine that would break Amazon's TOS.

Update 1:

Maybe. I wrote the original answer below earlier. I don't have time to look into this right now because I'm no longer on a project concerned with Amazon reviews, but their webpage at Product Advertising API states "The Product Advertising API helps you advertise Amazon products using product search and look up capability, product information and features such as Customer Reviews..." as of 2011-12-08. So I hope someone looks into it and posts back here; feel free to edit this answer.

Original:

Nope.

Here is an intersting forum discussion about the fact including theories as to why: http://forums.digitalpoint.com/showthread.php?t=1932326

If I'm wrong, please post what you find. I'm interested in getting the reviews content, as well as allowing submitting reviews to Amazon, if possible.

You might want to check this link: http://reviewazon.com/. I just stumbled across it and haven't looked into it, but I'm surprised I don't see any mention on their site about the update concerning the drop of Reviews from the Amazon Products Advertising API posted at: https://affiliate-program.amazon.com/gp/advertising/api/detail/main.html

Here's my quick take on it - you easily can retrieve the reviews themselves with a bit more work:

countries=['com','co.uk','ca','de']
books=[
        '''http://www.amazon.%s/Glass-House-Climate-Millennium-ebook/dp/B005U3U69C''',
        '''http://www.amazon.%s/The-Japanese-Observer-ebook/dp/B0078FMYD6''',
        '''http://www.amazon.%s/Falling-Through-Water-ebook/dp/B009VJ1622''',
      ]
import urllib2;
for book in books:
    print '-'*40
    print book.split('%s/')[1]
    for country in countries:
        asin=book.split('/')[-1]; title=book.split('/')[3]
        url='''http://www.amazon.%s/product-reviews/%s'''%(country,asin)
        try: f = urllib2.urlopen(url)
        except: page=""
        page=f.read().lower(); print '%s=%s'%(country, page.count('member-review'))
print '-'*40

According to Amazon Product Advertizing API License Agreement (https://affiliate-program.amazon.com/gp/advertising/api/detail/agreement.html) and specifically it's point 4.b.iii:

You will use Product Advertising Content only ... to send end users to and drive sales on the Amazon Site.

which means it's prohibited for you to show Amazon products reviews taken trough their API to sale products at your site. It's only allowed to redirect your site visitors to Amazon and get the affiliate commissions.