I've seen a lot of different thoughts about this recently, so I figured I'd offer my observations from my time working in Shenzhen for my IoT company.
Backstory: we’re partnered with Qualcomm to cloud enable bluetooth mesh technology across myriad US, Asian, and European based companies, primarily for lighting and smart home products in consumer/commercial markets. I spent about 6 months in Shenzhen and Hong Kong putting together the supply chain partnerships.
From what I’ve experienced, “brand,” i.e. the companies we’re familiar with as consumers, and Original Equipment Manufacturer “OEM” are used interchangeably, while Original Design Manufacturer “ODM” refers to the “factory.”
In most of my interactions, there is a tight albeit painful relationship between the OEM and ODM in consumer electronics because cooperation between multiple vendors is often required to get a product to market, especially in IoT. Typically, the most differentiated intellectual property (IP) is in the hands of the OEM (brand)— industrial design, software, firmware, and it’s in their best interests to obfuscate as much as possible throughout the supply chain to make it harder to replicate the technology, which everyone assumes will happen. And it does. This is especially true during the rise of the IoT, where connectivity challenges plague both sides of the pond, and clever solutions are the 11th hour superpower everyone is fighting to find first to use as leverage in the supply chain.
There is another class of manufacturers— not sure the technical name, but we call them “module makers” — companies that specialize in the design and production of drop-in PCB modules for various connectivity chipsets to make them easier to productize. An example would be ITON, who provides chips for several of GE’s products to the prime ODM (such as Leedarson or Eastfield) who is responsible for final assembly (note: many ODMs are also module makers— they keep chips in house to maximize control and profits).
Both ODMs and module makers participate in a process of product innovation that presupposes the market. Chipmakers (and other tech vendors) like Qualcomm send their reps out to the factories to demo new silicon technology in the form of a “reference design” in a bid to get the ODM to create a module or product based on that chipset that answers to a trend they’ve noticed from their OEM/brand customers. In this way, the ODM bears the R&D cost as a bet for business, but doing so gives them a chance to retain the right to get a royalty on every module sold. Ask an ODM to hand over any firmware they've made and they’ll tell you with their sweet puppy dog eyes “eat my shorts” because it’s how they keep you from just taking everything to another vendor.
For brands like Home Depot (or more generally companies less interested in designing hardware) these ODMs are essential because they are flexible enough to develop a catalog of partially developed products on speculation— whatever successfully sells up the food chain at Home Depot, they make real (note: the “make real” part is where a lot hits the fan because this stuff is hard to scale).
The OEM-ODM-module maker ecosystem creates a sort of “it takes a village to make a product” atmosphere, but with grumpy uncles, annoying neighbors, and meddling kids abounding. There's a constant sense of quiet espionage on both sides, although that tends to get better if you develop a direct relationship with your mfg partners. Western business has evolved to sustain trust with purely transactional relationships-- this is way less true in places like China. Go to lunch with them and take them to dinner a few times, invite them to Macau, get them drunk and having fun with you. These relationships are insurance policies on getting screwed. Further, having boots on the ground near your manufacturing is practically a requirement nowadays if you want to have any hope of your supply chain operating smoothly.
In the case of a brand like Apple, who meticulously defines and controls every little detail of their product and supply chain works with an Electronic Manufacturing Services company “EMS” like Foxconn who primarily invest only in building other designs precisely to specification.
So OEM v. EMS: OEM: “build this for me, exactly like this, and don’t ask too many questions, or I’ll eat your children.”
The ODM/OEM relationship is a bit shakier:
OEM: “build this for me, and pretty please do your best not to use lead paint or explode my users.”
All that said, many companies I’ve encountered are chimeric— companies that usually do business as an EMS could also be caught as an ODM if the opportunity is right. I’ve wracked my brain over how to approach meetings with ODMs that also have an OEM/brand side to the company. The ODM side is a potential partner while the OEM side is a potential customer— in the already confusing world of IoT this can be quite the rollercoaster.
I could be off, but the cash value of the above has navigated me through hella lots of conversations from ivory tower to where the dog food gets made. It is a truly global and complex web of associations, across cultural, language, political, and social boundaries. Read “Poorly Made in China” and “Barbarians at the Gate” to see the differences in East vs. West strategies for business success, which I see as orthogonal values of Replication and Dominance.
If you’re interested, here’s a great article by a Shenzhen based supply chain expert: https://www.linkedin.com/pulse/3-types-partners-product-managers-can-use-development-changtsong-lin/