Bis(ylidyl)phosphanes can be prepared from ylides and dichlorophosphanes or from bis-(ylidyl)phosphenium chlorides and organolithium compounds. By substituting in bis(ylidyl)-phosphenium chlorides the chloride ion for more basic anions, a large variety of bis(ylidyl)-phosphanes is accessible. They can be protonated at the ylidic carbon atoms, but alkylated and oxidized at the central phosphorus atom. As shown by 31P NM R in solution and by X-ray investigation of the crystal, the lone pair at the tervalent phosphorus is generally oriented synperiplanar to both phosphonio groups.