From the earliest days of railways, many wagons were built for different purposes and some of these types became quite distinct and instantly recognisable such as cattle wagons, whilst others evolved over time, like coal wagons. Summarising the main types of LNWR wagons is more difficult than some other railways because the LNWR could trace its roots back to the very first railways, so we are discussing a period of almost 100 years from 1825 to 1923.

As with other railways, in addition to standard open wagons, vans and coal wagons, the location of traffic generating business had an impact on the types of wagons built. For example, the largest manufacturer of sheet (later plate) glass was Pilkington at St.Helens which was on the LNWR and as a consequence the LNWR had more glass wagons than any other railway. That business also needed sand which resulted in the LNWR's D10 sand wagons. Beer, slate and tramcars were also niche businesses which were important to the LNWR. The largest quantity of goods carried by train was coal, but the LNWR had relatively few traffic coal wagons because most of the coal wagons were owned by collieries, coal factors and coal merchants. These had to be approved and registered by a railway company but were rarely owned by that company.

J.Watson Emmett was Wagon Superintendent at Earlestown from 1867 to 1903, when he was succeeded by H.D.Earl. This, together with the Chairman's preference for shareholder profit over technical innovation probably explains the continuity of designs during that period. It probably also explains why some designs had become a little old fashioned by the time he retired, some having increased in length from 15ft through 15ft 6in to 16ft, but otherwise little changed. In the crucial 1902-1903 changeover period the wagon diagram book was produced, which forms the basis of this work. That period is also when several experimental larger wagons and vans were produced, some one-offs and others small quantities, until the standard was set as an 18ft wagon with 9ft 9in wheelbase.

The pages of the 1903 Diagram Book were numbered from 1 to 83. Different types of wagon soon became known as "page number x", or more usually, "Diagram x", or "Dx". The purpose of the diagram book was for staff to know the capacity of each type. When an item was consigned, staff needed to know that it would fit in a particular wagon type, so the internal dimensions and load capacity were important whereas its appearance was not.

Immediately after 1903, new wagon types were allocated a new page with a suffix - such as D17a and in the case of locomotive coal wagons these suffixes went up to "d". But very soon new numbers were allocated at the back of the book, the page numbers reaching 110 by 1923. Unlike the LNWR's carriage diagram books which were issued in 1893 and then entirely superseded in 1903 and again in 1915, the wagon diagram book was never replaced, so its numbers remained constant for the remainder of the company's separate existence. (there had been a diagram book of special trollies drawn up in 1894 but that does not detract from the points made here).

The quantity of wagons built and owned by the LNWR is quite staggering. In 1862 they started accounting for new wagons in the same way that they did locomotives, carriages and most other assets - replacements were charged to a revenue account and those wagons took the numbers of the vehicles being replaced. Additions were charged to a capital account and took the first available spare numbers. In 1862 there were almost 18,000 wagons and by 1923 it was approaching 80,000. That is the number in service at that time, so allowing for replacements over the decades the total wagons built by the LNWR during the company's separate existence was probably over a quarter of a million! The vast majority of those were built by the LNWR in its own workshops at Earlestown. Lancashire.