The head of the Vichy state and government was Philippe Pétain, a formerly popular World War I commander. In fact, many Frenchmen hoped that Pétain’s submission was just a ruse, and he was planning an uprising to throw the Germans out. In contrast, Charles de Gaulle, who is today identified with French contributions to the Allied war effort, was a largely unknown officer who fled to the safety of Britain, was raising trouble from overseas and was court-martialed and sentenced to death in absentia. As the oppressive reality of German occupation started to become manifest, the seeds of resistance started to sprout. Here’s an overview of the main resistance groups.
 
The French government and intelligence services
Surprisingly, the Vichy government itself hid resistance members. The Deuxième Bureau de l'État-major general (“Second Bureau of the General Staff”), France’s external intelligence organization, remained loyal to the Allied cause even though they fell under the control of the new collaborationist government. It continued to collect intelligence on Germany and passed it on to British intelligence. The bureau knew very well that Polish codebreakers had already broken an earlier version of the German Enigma cypher, but kept this information secret from Germany – as a result, Germany kept using Enigma throughout the war, allowing vital messages to be decoded by British cryptologists working at Bletchley Park. Meanwhile, the counter-intelligence section continued to look for and arrest German agents.

The French military
The remains of the armed forces of France were in a bind. They naturally loathed German occupation and wanted to keep fighting, but were bound by the chain of command and had to follow Pétain’s directives, to whom they were steadfastly loyal thanks to his importance in World War I. Germany was watching French soldiers with a hawkish eye, and anyone displaying signs of disloyalty quickly found his family deported to Germany as hostages.
 
Nevertheless, the army made preparations for a resurgence. One Colonel Jean Touzet du Vigier recruited reservist officers to create hidden caches of equipment ranking from ammunition to entire tanks kept in barns. Later on, many Resistance groups lamented the army’s reluctance to share these caches with them.

Communists
The French Communist Party (PCF) was in a perilous place in 1939. After the Molotov-Ribbentrop Pact between the Soviet Union and Nazi Germany, the party was proscribed in France and many of its leaders arrested or forced to go underground. Meanwhile, the Communist International in Moscow ordered the remains of the party to honor the new Soviet-Nazi nonaggression agreement even after Germany invaded France. The party was split between those who wanted to act against the occupiers and those who toed the prescribed line of neutrality. 

Things changed with the 1941 German invasion of the Soviet Union, after which the Nazis were fair game. French communists were among the first Resistance groups to use open violence against the German occupiers, and many of the members already gained experienced with clandestine warfare during their participation in the Spanish Civil War on the Republican side. 

The first act of overt violence by the Communists occurred on August 21, 1941, when Colonel Pierre-Georges Fabien shot and killed a German officer at a metro station in Paris. Other similar assassinations followed, prompting the Germans to establish a policy according to which every assassinated German soldier must be avenged by the execution of a large number of French civilians. The policy precipitated a moral crisis in the Resistance. Some believed that further assassinations were immoral as they led to innocent deaths; the Communists accepted the price as fair, as German brutality would push even more people into joining the Resistance.
 
The armed branch of the PCF were the Francs-tireurs et partisans français (“French freeshooters and partisans,” FTP). The FTP operated under Communist control, but non-Communists were also welcome to join. FTP groups operated in highly compartmentalized cells to prevent a single capture freedom fighter from betraying the entire network. Each local group consisted of eight men: a group leader directly commanding three men, and an “assistant” commanding three others and reporting to the group leader. Four such combat groups could be temporarily joined into a detachment, multiple detachments into a company, and several companies into a battalion. Larger units only assembled just prior to an attack, and dispersed immediately afterwards. Every individual combatant had his own hiding place, the location of which even his own group leader did not know. FTP combat groups were brutally effective. On one occasion, they threw a grenade in the back of a lorry carrying 30 Germans. They once threw a grenade in a restaurant frequented by German officers; mined roads, attacked trains and machine-gunned German troops. They proved that the Germans were vulnerable and could never relax in occupied territory. Eventually, the FTP became one of the major groups to form the French Forces of the Interior.

Gaullists
As mentioned above, de Gaulle was little-known at the beginning of the war, and he fled to Britain to form his government-in-exile there. Nevertheless, he slowly started making waves in occupied France, in large part thanks to his radio messages broadcast by the BBC. In November 1940, 3,000 students protesting at the Arc de Triomphe shouted “Vive de Gaulle” alongside “Vive la France.” Some only shouted “Vive” then brandished two fishing rods high in the air as a pun – “two fishing rods” is “deux gaules” in French.

Many of de Gaulle’s supporters ended up escaping to Britain and joining the war as regular soldiers of Free France, fighting on many battlefields. Most Gaullists, however, could not escape and had to stay in France. Since Britain recognized de Gaulle as the legitimate leader of France, Gaullist resistance groups usually received preferential treatment over Communists when it came to distributing the limited amount of weapons and supplies Britain could distribute by air drops.
 
In time, de Gaulle came to dominate the top-level support for the Resistance. This was largely due to the work of Jean Moulin, a former civil servant who escaped to Britain and received de Gaulle’s blessing on his plan to unify the largest and most powerful Resistance groups. After traveling back to France, Moulin established a network which eventually grouped the eight most important groups (including the FTP and Combat, see below under “Nationalists”) into the National Council of the Resistance.

Nationalists
France had its share of far-right political movements between the two World Wars. These movements preached various mixtures of nationalism, monarchism, anti-parliamentarism, anti-Semitism and outright fascism. The German invasion violently stirred the pot. The Nazi regime was exactly the sort of far-right state many French nationalists have been espousing – and many French nationalists earnestly welcomed the Vichy State –, but, of course, it was German, imposed on an oppressed French people by an outside invader. Some men, the so-called Vichyst-resisters (“Vichysto-résistant”) accepted Pétain, at least up until the German occupation of the Free Zone, but rejected the Vichy regime for being a German puppet.