Why does Google show old title?

[eli.boda]

I made some changes to title tags on a clients site over a month ago. Google has since crawled all the pages that the changes were made to.

Here's the problem. For some of the pages, the old title is still showing in search results.

1. Why does Google do this? 2) What can I do about it?

[SanketPatel]

Hi

Are you sure your old title is showing in SERP or its showing different title ?

Ans :

"Google's generation of page titles and descriptions (or "snippets") is completely automated and takes into account both the content of a page as well as references to it that appear on the web. The goal of the snippet and title is to best represent and describe each result and explain how it relates to the user's query."

Above given statement are from Google Webmaster Help.. Please read for more info : http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35624

[eli.boda]

Yes I'm sure it's the old title.

I guess it's possible that Google liked the old title better and is just ignoring the change?

I'll do some digging and see if I can find anything on the subject. Please share any resources you can find that address this

[SanketPatel]

Google uses many signals to show title in SERP like social signals, title used in directories, backlink profile of that page etc.

I think this is only an authoritative resource for this topic:  http://support.google.com/webmasters/bin/answer.py?hl=en&answer=35624