Many manufacturing industries have made great gains by utilizing lean principles in the factory. These principles, which have perhaps been most successfully applied in the Toyota Production System, can be summarized as follows:

1. All work must be clearly defined as to content, sequence, timing, and outcome.
2. Every customer-supplier connection must be direct, explicit, and transparent
3. An effective protocol must be used to communicate requests and information about deliveries and priorities.
4. The pathway for delivering every product and service must be simple, seamless, and well understood by the responsible agents.
5. Improvements must be guided through carefully controlled experiments, under the guidance of an experienced coach, at have ownership at the lowest possible levels in the responsible groups.

Lean means the elimination of waste. In manufacturing, this typically means reduction of material in inventory, since that material is expensive, and since such reductions cause efficiencies in other important aspects, such as cycle time. In knowledge-based industries, waste is not extra people, as you might expect, but rather a reduction in the information and decisions that are 'in inventory', or essentially, in processing.  This waste reduction is usually further augmented with additional efficiency improvements, by balancing capacity against demand, and prioritizing work queues.

Lean practices have not yet made the penetration within engineering groups that they have achieved in manufacturing. I believe this is for several reasons. The first reason is that engineers don't always understand why cycle time is important to business; this article is a good summary of why competitiveness is so dependent upon this factor. The second reason is the lack of a clear and brief explanation of how lean principles can be applied to the engineering environment. I believe this need is effectively addressed by this presentation by Alistair Cockburn, though such agile techniques will only help kickstart a group on its lean journey. The third reason for this lack of penetration is because there haven't yet been enough good examples and 'how-to' guidance available or shared on lean practices that have been relevant to engineering fields. As a result, many groups think lean practices are not relevant to what they do, believe that lean is a way of thinking, rather than a collection of techniques, or do not know what steps they might take to employ these techniques. 

I believe the most important reason that lean techniques have not had the penetration within engineering as it has in manufacturing environments is because variation in manufacturing results when precedented, mechanistic operations are implemented inconsistently. Within engineering, by definition, such operations do not exist. Each engineering problem is unique, and requires a search through unknown territory. This search can be more efficient when it is well structured, and better outcomes can be achieved, but variation in time and outcomes is inevitable.