The Sales Funnel is a very popular method of visualising a buyer's journey from being unknown, through to being a customer.
However, as Neil Curtis of NTT points out, one of the most important steps is involving Sales, not only in the design of the process but also in the feedback.
In organisations where the Sales process is both complicated and consultative, there is a temptation for marketing to move prospects from being "Marketing Qualified Leads" (MQLs) to being "Sales Qualified Leads" (SQLs); a process which often involves passing a lead from a marketing automation platform to a CRM at which point Marketing are "done". Sales take over and either close the prospect or send them back to an earlier stage of the funnel for another try.
However, this is often an overly simplistic view of the process. What is really important is for Sales to communicate to those creating content what the industry issues the potential client is facing today. That way, the Subject Matter Experts can address these concerns specifically in order to help their Sales people advance existing prospects, right up to the point of close.
You need to define the funnel and its economics, design processes and workflow, agree lead handover contracts with sales as well as measurement, reporting and feedback loops — and enable continuous improvement. Focus on getting good data into your CRM — good in, good out.