From the original plain white tilework and Art Nouveau entrances, the architecture of Paris Métro stations has evolved with successive waves of building and renovation.

The CMP was concerned to avoid criticism in the context of a backlash against the industrial-style architecture epitomized by the recently built Eiffel Tower.

Built in cast iron, they make heavy reference to the symbolism of plants and are now considered classic examples of French Art Nouveau architecture.

The simpler open type of entrance, known as an entourage (enclosure), is framed by a "Métropolitain" sign held between two ornate, sinuously curved lampposts.

These are designed strikingly in the form of plant stems, in which the orange lamp is enclosed by a leaf (resembling a brin de muguet, or sprig of lily of the valley).

[4]: 73 From 1904, the CMP employed the architect Joseph Cassien-Bernard to design a number of new station entrances in austere neo-classical stonework.

Many of the entrances that were built by the Nord-Sud company on the present-day lines 12 and 13 retain elegant Art Nouveau style motifs on the tiling surrounding the walls of the stairwell.

The simpler, Art Deco-inspired Dervaux lampposts (named after their architect) became common in the 1930s, following the contemporary trend away from decorative embellishment.

Masts built since 1998 on line 14 are almost entirely novel, featuring a minimalist two-dimensional design but containing a hint of the original Guimard style in their plant-like verticals.

From the 1930s, network maps appeared, including the popular plan indicateur lumineux d'itinéraires, a version with lights to indicate the fastest route to a given destination.

Elevators were first installed at République in 1910, following a convention by which the CMP agreed to build them where platforms were situated deeper than 12 m below street level.

Automatic crowd-control gates known as portillons automatiques were once present in the majority of stations at the end of the corridors leading to the platforms.

They are larger, allowing for straight walls up to the point where the curvature of the vault begins, and have higher ceilings to provide room for overhead catenaries that have since been removed.

Early stations built by cut-and-cover (due to tracks being less than 7 m (23 ft) below the surface) typically feature roofs of metal beams, which in turn support miniature brickwork vaulting (as at Champs-Élysées – Clemenceau on line 1).

A second type of cut-and-cover train hall is found in suburban stations built after the Second World War, and has a pure rectangular cross-section and reinforced concrete construction (for example, Malakoff – Plateau de Vanves).

There are a number of stations on line 12, including Falguière and Convention, whose Nord-Sud tiling is intact but has been covered over and hidden from view since renovation in carrossage style in the 1960s (see below).

The CMP rolled out its final chosen design in 1921 in three newly built line 3 (now 3bis) stations from Gambetta to Porte des Lilas.

The CMP also tiled its poster frames with more elaborately decorated borders of honey or ochre-colored faience, featuring floral and organic motifs.

This proved to be cheaper than refurbishing the tile and increased the amount of space available for advertising posters whose revenues contributed to financing the renovation.

It used space on the platforms, making stations feel more cramped, and it rendered maintenance of the underlying tilework difficult.

Neither of these experiments was repeated elsewhere, but by the end of the decade the RATP had settled on a new renovation style known as Mouton-Duvernet (this eponymous station on line 4 being the first concerned).

Flat, non-bevelled orange tiles covered the station walls but not the roof, which was simply painted in a neutral (and often dark) tone.

To introduce color into the stations, a coordinated colour scheme was added to elements of the train hall – the seating, light housings, and walls of connecting corridors.

With the RATP's commitment in the 2010s to progressively install energy-saving light-emitting diodes LEDs throughout the metro network, it has now become possible to restore color to Ouï-dire stations.

The decoration of Mairie de Montrouge station, opened in 2013 on line 4, includes elements of the Météor style alongside entirely new features such as corrugated metal panelling.

This extremely successful style has been used by the RATP in all of the major station renovations undertaken since 1999 as part of the Renouveau du Métro program.

This light fixture has the benefit of being equally bright as the Gaudin model, but is very discreet, and allows the RATP to work around the particularities of many stations.

Starting in 1999, and in conjunction with the Bruno-Gaudin architectural charter developed in the late 1990s, the RATP has been conducting a major programme of station renovation, known as Le Renouveau du Métro.

Despite the CMP's later decision to equip future stations with tiled nameplates, the enamel plaques in place survived well into the postwar period, with the last example, at La Motte-Picquet – Grenelle on line 6, only retired in 2006.

In the early 1970s, spurred on by the development of the RER system and by the opening of several new extensions to the network, the RATP undertook a program to harmonize the metro's corporate identity by replacing the many different fonts then in use with a unified, standard typeface.