Analytics How to track conversions when the purchase cycle is long and happens through multiple devices?

There are a few ways of going about this. Web Analytics If you are using Google Analytics the 'utmz'  cookie which stores visitor source has a default 6 month expiration. So if a user clicks on an AdWords ad in Jan then converts in June you will be able to tie it back to the original source using just the default attribution reports. The sma eis probably true with other web analytics tools though I'm not so familiar with them. Though obviously that doesn't help if they convert on a different machine, browser or have cleared their cookies in the mean time. Offline reporting If you capture lead immediately from the click, you can also capture a source code parameter from the destination URL, e.g. ?source=GoogleAdWordsCampainXYZ123, store that in a cookie and then pass it with form submission in to a record. Then do a match-back on email address or first and last name etc from a bulk export of your sales to your initial leads to attribute sales by referring channel. This is probably the most robust approach and one that most sophisticated eCommerce of online to offline business take. The Zen approach In practice, you and every other advertiser (even the biggest advertisers in the world) will never fully understand where your customer come from or why they are buying, especially with such a long buying cycle. The best you can do is try to make informed decisions, if for example you know that a typical lead time is 3 -6 months, then you need to take your faith in both hands, spend generate an appreciable number of leads, then look for a Year on-Year increase in sales in the next 6 months. If you can see this then you will be able to further increase spend and so on. If you have sufficient spend and the offline reporting as description above in place you can use a mathematical regression analysis to understand how the channels interrelate - but be prepared to pay a stats jock $20k+ to build and maintain this model.

You can pull a multichannel report, such as first click / last click conversions and track down the conversion journey. Bad news are that unless you manage to save the email of this user on the first interaction the moment it changes device it will be seen a fresh new user...

Do you have a piece of uniquely identifiable information? Such as the user's email address? If you do set a "custom variable" that has that user's email address as that value. Then you can run a report that includes that variable and when they first came to your website. https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingCustomVariables

If you want Google Analytics to keep the first referrer as the source of a conversion after the visitor has returned through other channels, you can use the "&utm_nooverride=1" value: http://productforums.google.com/forum/#!topic/analytics/ITlAfbqUQMw Good luck!