Industry (17)
http://www.worldheritagesite.org/categories/category49.html

Crespi d'Adda
Derwent
Engelsberg
Fagus
Falun
Fray Bentos
Humberstone
Ironbridge
New Lanark
Red Bay
Rjukan
Arc-et-Senans
Meiji
Tomioka
Van Nellefabriek
Voelkingen
Verla

Ironbridge Gorge - the symbol of the Industrial Revolution
Falun - oldest still-existing copper mining enterprise in the world, since at least the 14th century; Technological developments at the mine had a profound influence on mining globally for two centuries
Arc-et-Senans - ideal industrialized landscape

I've visited most of the ones above, but most are only of niche interest. Maybe add Völklingen (modern ironmaking)

Arc et senans (underground salt extraction)
Ironbridge gorge
Zollverein

My selection:

Falun
Ironbridge
New Lanark
Meiji

My selection:
Falun
Ironbridge
Arc-et-Senans
Meiji

Ironbridge
Arc-et-Senans

Hard category, as I like all of them.
* Derwent: Ever more complex mills showing the progress in the industrialization.
* Fagus: Great architecture.
* Meiji: Gives you a feeling how backwards Japan was and how much catching up they did in the 1900s.
* Voelkingen: Great iron work.

I really want to choose iconic Ironbridge but the site is really underwhelmed! I prefer Volklingen as ideal image of industrial site or Falun for mining example.

Mines of Rammelsberg
Falun
Wieliczka
Ironbridge
Crespi d'Adda

1. Ironbridge Gorge -- iconic symbol of the Industrial Revolution; historic village and a valley rich in coal, iron ore, limestone, and clay, leading to the development of an iron industry
2. Völklingen Ironworks -- epitomizes the steel-making industry, vital to the development of infrastructure and transportation
3. New Lanark -- philanthropist town centered around the cotton mill industry, highlighting textile production
4. Tomioka Silk Mill -- highlights the silk-making process, as well as Japan's entry into the industrialized world
5. Fray Bentos -- I know this isn't a popular choice, but the meat-packing industry probably should be highlighted for its impact on global dining habits
6. Rjukan / Notodden -- showcases the power industry through the harnessing of waterfalls and rivers for hydroelectric power

I'd love to include the salt industry here, but I think Wieliczka from the Mines category is really the better choice.

Summarizing:

Crespi d'Adda (also under Urban Planning, where it currently stands as a 'No')
Derwent
Engelsberg
Fagus
Falun - oldest still-existing copper mining enterprise in the world, since at least the 14th century
Fray Bentos
Humberstone
Ironbridge - the symbol of the Industrial Revolution
New Lanark - philanthropist town centered around the cotton mill industry, highlighting textile production (also under Urban Planning, where it currently stands as a 'Yes')
Red Bay
Rjukan
Arc-et-Senans - ideal industrialized landscape, underground salt extraction
Meiji
Tomioka
Van Nellefabriek
Voelkingen - epitomizes the steel-making industry,
Verla

There's a similar category 'Mines', where only Falun doubles. I prefer to keep these two categories separated.

A Pedant's point - Volklingen has nothing to do with "Steel-making industry" - only with Iron making! It could at a stretch, be said to represent "Iron and Steel production". Its comparators are Engelsberg and Ironbridge - 3 different stages in the development of Iron making. How many ironmaking sites do we need?

Van Nellefabriek stands or falls on its architectural merit/significance. I know it represents an improvement in the working conditions of factory workers between the Wars and in rational design of factories to optimise production but I would regard these as very subsidiary "merits". Fagus would do as well wouldn't it?

Meiji seems to have received more support than I might have expected. I have only seen the Glover House Park and the Crane and Slipways around Nagaski together with a distant view of Battleship Island. The "Industrialisation of Japan" over such a short period seems very significant when looked at from the point of view of WWII but, in the longer view, does its significance not recede somewhat? Why is the spread of the Industrial Revolution to Japan so important? Not so much in its own right perhaps as for representing the spread of industry beyond Europe? I am not sure. As for what is "on show" - Only the Glover house is "authentic" in its site and the other locations are pretty minimal in terms of importance aren't they?

Many of the rest are just representatives of different products. We have a similar problem as with different types of agricultural crops - one can build up a large list of different manufactured items and the sites where they were produced at different times in history. In a list extending to 1000..... etc many different types of product can be covered (and no doubt will be in future!) but in a list of 400 how do we bring out the "most important". Indeed how many from this category should we be thinking of keeping? If we hit the overall average of 40% we would need no more than 7!

I would look for coverage on 2 factors
a. The most important/primary industries
b. A representation of manufacturing across the centuries - but giving primacy to where something major happened for the first time

So
1. Ironbridge - yes I know that much of the site is very touristy in its presentation but the Bridge alone justifies it. And it can represent early Iron making thus excluding Engelsberg at least
2. Derwent or Lanark - Both early weaving enterprises . Each has much the same "presentation" problem as with Ironbridge. Derwent has the benefit of being more significant as the start of the production process but Lanark offers "social" vision and philanthropy - though both cover early industrial housing.
3. Volklingen - another iron making site but shows how industry in general has developed by the late 19thC
4. Humberstone or Fray Bentos - to represent the worldwide impact of industrialisation/trade
5. Rjukan - to represent the introduction of electricity as a power source in 20th C

I will leave the final 1 or 2 to others!

Wrapping this one up:

Crespi d'Adda (also under Urban Planning, where it currently stands as a 'No')
Derwent - early weaving Enterprise, start of the production process, early Industrial housing
Engelsberg
Fagus
Falun - oldest still-existing copper mining enterprise in the world, since at least the 14th century
Fray Bentos - to represent the worldwide impact of industrialisation/trade
Humberstone
Ironbridge - the symbol of the Industrial Revolution, represents early Iron making
New Lanark - philanthropist town centered around the cotton mill industry, highlighting textile production (also under Urban Planning, where it currently stands as a 'Yes')
Red Bay
Rjukan - showcases the 20th century power industry through the harnessing of waterfalls and rivers for hydroelectric power
Arc-et-Senans - ideal industrialized landscape, underground salt extraction
Meiji - Gives you a feeling how backwards Japan was and how much catching up they did in the 1900s.
Tomioka
Van Nellefabriek
Voelkingen - epitomizes the modern iron-making industry,
Verla

@Solivagant -- you're right, steel actually wasn't made at Völklingen Ironworks, and it's better defined as a more modern iron-making site. Good catch!