By the time the campaign began, Napoleon was able to boast an army of around 124,000 men. Although this contained many raw recruits, it was bolstered by the return of battle-hardened veterans, most of whom were deployed in the Imperial Guard. The army was organised into two powerful wings and a central reserve. The left wing was commanded by Michel Ney, 'the bravest of the brave', the right wing commanded by the Marquis de Grouchy. He was an undistinguished leader and his appointment seems to highlight the lack of resources being suffered by Napoleon in terms of generals. As Chief of Staff, Napoleon appointed Soult. It has been argued that this was also a mistake, as Soult would have been far more capable as a corp commander.
Wellington and Blucher set out a number of agreements which cemented their mutual respect and understanding
Wellington and Blucher commanded a combination of troops from several different countries, totalling around 94,000 British, Dutch and Hanoverians and 123,000 Prussians. However, these troops were dotted right across Belgium, with Blucher and his Prussians holding the east and Wellington controlling the west including Brussels. On taking charge of his heterogeneous force, Wellington immediately set about trying to mould them into a coherent army. He obtained more veteran British troops and endeavoured to integrate these throughout the army so that all units of questionable quality and experience were flanked by more stable troops. At this stage, Wellington and Blucher set out a number of agreements which cemented their mutual respect and understanding and proved to be crucial to the outcome of the campaign: an interarmy boundary was drawn up along the Roman road from Bavay to Maastricht, concentration points finalised for the two armies (Nivelles for Wellington and Sombreffe for Blucher), liaison staff were exchanged with provision made for the passage of intelligence and both generals resolved to support the other if attacked.