Alfred Waterhouse RA PPRIBA (19 July 1830 – 22 August 1905) was an English architect, particularly associated with Gothic Revival architecture, although he designed using other architectural styles as well. He is perhaps best known for his designs for Manchester Town Hall and the Natural History Museum in London. He designed other town halls, the Manchester Assize buildings—bombed in World War II—and the adjacent Strangeways Prison. He also designed several hospitals, the most architecturally interesting being the Royal Infirmary Liverpool and University College Hospital London. He was particularly active in designing buildings for universities, including both Oxford and Cambridge but also what became Liverpool, Manchester and Leeds universities. He designed many country houses, the most important being Eaton Hall in Cheshire. He designed several bank buildings and offices for insurance companies, most notably the Prudential Assurance Company. Although not a major church designer he produced several notable churches and chapels.

Financially speaking, Waterhouse was probably the most successful of all Victorian architects. He designed some of the most expensive buildings of the Victorian age. The three most costly were Manchester Town Hall, Eaton Hall and the Natural History Museum; they were also among the largest buildings of their type built during the period. Waterhouse had a reputation for being able to plan logically laid out buildings, often on awkward or cramped sites. He built soundly constructed buildings, having built up a well structured and organised architectural office, and used reliable sub-contractors and suppliers. His versatility in stylistic matters also attracted clients. Though expert within Neo-Gothic, Renaissance Revival and Romanesque Revival styles, Waterhouse never limited himself to a single architectural style. He often used eclecticism in his buildings. Styles that he used occasionally include Tudor revival, Jacobethan, Italianate, and some only once or twice, such as Scottish baronial architecture, Baroque Revival, Queen Anne style architecture and Neoclassical architecture.

As with the architectural styles he used when designing his buildings, the materials and decoration also show the use of diverse materials. Waterhouse is known for the use of terracotta on the exterior of his buildings, most famously at the Natural History Museum. He also used faience, once its mass production was possible, on the interiors of his buildings. But he also used brick, often a combination of different colours, or with other materials such as terracotta and stone. This was especially the case with his buildings for the Prudential Assurance Company, educational, hospital and domestic buildings. In his Manchester Assize Courts, he used different coloured stones externally to decorate it. At Manchester Town Hall and Eaton Hall the exterior walls are almost entirely of a single type of stone. His interiors ranged from the most elaborate at Eaton Hall and Manchester Town Hall, respectively for Britain's richest man and northern England's richest city cottonopolis, to the simplest in buildings like the Royal Liverpool Infirmary, where utility and hygiene dictated the interior design, and the even starker Strangeways Prison.

His father was Alfred Waterhouse Senior (1798–1873), a cotton broker, and his mother was Mary Waterhouse, née Bevan (1805–1880), of Tottenham, both Quakers. Alfred, first of their eight children, was born on 19 July 1830 when the family was living at Stone Hill, Liverpool. Shortly after his birth, the family moved to Oakfield, a Tudor-style villa in Aigburth, Liverpool, Lancashire. His brothers were accountant Edwin Waterhouse (1841–1917), co-founder of the Price Waterhouse partnership, which now forms part of PriceWaterhouseCoopers, and solicitor Theodore Waterhouse (1838–1891), who founded the law firm Waterhouse & Co, now part of Field Fisher Waterhouse LLP in the City of London. Alfred Waterhouse was educated at the Quaker Grove House School in Tottenham, later to become Leighton Park School.

He began his architectural studies in 1848 under Richard Lane in Manchester. He was taught to produce architectural drawings with crisp lines and pale tints, very different from the style he would develop later. He was taught theory by copying extracts from books, including Henry William Inwood's Of the Resources of Design in the Architecture of Greece, Egypt, and other Countries, obtained by the Studies of the Architects of those Countries from Nature (1834) and William Chamber's A treatise on civil architecture (1759). He also traced the designs in Frederick Apthorp Paley's Manual of Gothic Mouldings (1845). The scrapbook he used survives in which he sets out Chambers and Paley's opposing views. He is also known to have read during this period John Ruskin's The Stones of Venice (1849) and Augustus Pugin's Contrasts (1836) and The True Principles of Pointed or Christian Architecture (1841). He joined a sketching club, where he met Frederic Shields and Alfred Darbyshire.

In May 1853 he set out to tour Europe with school friend Thomas Hodgkin who stated that Waterhouse "was entirely under the influence of Ruskin, and communicated his own admiration for Gothic art and a perfect detestation of that beastly Renaissance". The trip lasted nine months. Sailing to Dieppe, passing through Rouen, then Paris, taking a steamer from Dijon down the Saône to Lyon, then on to Nîmes, Arles and Orange. Staying the night at the Grande Chartreuse, passing into Piedmont to Susa and Turin, they walked over the Great St Bernard Pass in a snowstorm into Switzerland. In Basel Waterhouse parted company with Hodgkin and returned to Italy in the company of a Manchester acquaintance George Rooke. Waterhouse's sketchbook from the trip survives and is titled Scraps from France, Switzerland, and Italy. Every notebook sketch is dated and labelled so his itinerary can be followed. In Italy he visited Isola Bella, Certosa di Pavia, Milan, Bergamo, Monza and Venice where he remained for two weeks in August. Here he sketched the Doge's Palace and St Mark's Basilica. The tour continued in Padua, Vicenza and Verona. By the end of September he arrived in Florence, where he stayed a week, sketching Giotto's Campanile, amongst other buildings. He continued via Siena, Fiesole, Lucca and Pisa to Naples, where he stayed around three weeks and toured surrounding towns. In November he arrived in Rome and stayed into the new year. Returning to northern Italy he revisited several cities before passing through Turin on the way to Basel and Strasbourg.

Much later in life, Waterhouse in his 1890 presidential address at the RIBA had this to say about sketching by architectural students:

If the architect-student knew that it is not by mere number and beauty of his sketches, and by the accuracy of his measured drawings of old edifices, that he could satisfy those who sent him forth on his travels, but by the proofs he was able to afford that he had absorbed and digested what he had seen,....men would be more ready designers after having had such preparation. Having got the ancient examples into their heads, instead of merely in their sketchbooks, they would learn to lean not on illustrations and other extraneous help, but on what had become part of themselves, and so prove not mere copyists, but self-reliant and original designers."