The Belgian Resistance (French: Résistance belge, Dutch: Belgisch verzet) collectively refers to the resistance movements opposed to the German occupation of Belgium during World War II. Within Belgium, resistance was fragmented between many separate organizations, divided by region and political stances. The resistance included both men and women from both Walloon and Flemish parts of the country. Aside from sabotage of military infrastructure in the country and assassinations of collaborators, these groups also published large numbers of underground newspapers, gathered intelligence and maintained various escape networks that helped Allied airmen trapped behind enemy lines escape from German-occupied Europe.

During the war, it is estimated that approximately five percent of the national population were involved in some form of resistance activity, while some estimates put the number of resistance members killed at over 19,000; roughly 25 percent of its "active" members.

German forces invaded Belgium, which had been following a policy of neutrality, on 10 May 1940. After 18 days of fighting, the Belgian Army surrendered on 28 May and the country was placed under German military occupation. During the fighting, between 600,000 and 650,000 Belgian men (nearly 20 percent of the country's male population) served in the military. Many were made prisoners of war and detained in camps in Germany, although some were released before the end of the war. Leopold III, king and commander-in-chief of the army, also surrendered to the Germans on 28 May along with his army and was also held prisoner by the Germans. On 18 June the Belgian Government fled and arrived first in Bordeaux, France after the French government had fled to the region three days earlier. On that same day the Belgian government sent a telegram to the imprisoned Belgian king, stating their resignation to the king. Marcel-Henri Jaspar, the Belgian Minister of Health, went to London on 21 June without the permission of the government. He later gave a speech on BBC Radio on 23 June stating he would continue to fight against the Germans. Three days later the Belgian government stripped his ministerial title in reaction to the speech.

Among the first members of the Belgian resistance were former soldiers, and in particular officers, who, on their return from prisoner of war camps, wished to continue the fight against the Germans out of patriotism. Nevertheless, resistance was slow to develop in the first few months of the occupation because it seemed that German victory was imminent. The German failure to invade Great Britain, coupled with aggravating German policies within occupied Belgium, especially the persecution of Belgian Jews and conscription of Belgian civilians into forced labour programmes, increasingly turned patriotic Belgian civilians from liberal or Catholic backgrounds against the German regime and towards the resistance. With the German invasion of the Soviet Union in June 1941, members of the Communist Party, which had previously been ambivalent towards both Allied and Axis sides, also joined the resistance en masse, forming their own separate groups calling for a "national uprising" against Nazi rule. During the First World War, Belgium had been occupied by Germany for four years and had developed an effective network of resistance, which provided key inspiration for the formation of similar groups in 1940.

Most of the resistance was focused in the French-speaking areas of Belgium (Wallonia and the city of Brussels), although Flemish involvement in the resistance was also significant. Around 70 percent of underground newspapers were in French, while 60 percent of political prisoners were Walloon.

The most widespread form of resistance in occupied Belgium was non-violent. Listening to Radio Belgique broadcasts from London, which was officially prohibited by the German occupiers, was a common form of passive resistance, but civil disobedience in particular was employed. This was often carried out by Belgian government institutions that were forced to carry out the administration of the territory on behalf of the German military government. In June 1941, the City Council of Brussels refused to distribute Star of David badges on behalf of the German government to Belgian Jews.

Striking was the most common form of passive resistance and often took place on symbolic dates, such as the 10 May (anniversary of the German invasion), 21 July (National Day) and 11 November (anniversary of the German surrender in World War I). The largest was the so-called "Strike of the 100,000", which broke out on 10 May 1941 in the Cockerill steel works in Seraing. News of the strike spread rapidly and soon at least 70,000 workers came out on strike across the province of Liège. The Germans increased workers' salaries by eight percent and the strike finished rapidly. Future large-scale strikes were repressed by the Germans, although further important strikes occurred in November 1942 and February 1943.

King Leopold III, imprisoned in Laeken Palace, became a focal point for passive resistance, despite having been condemned by the government-in-exile for his decision to surrender.