This paper presents a 3-D shape-adaptive directional wavelet coding technique for object-based scalable video coding. This technique includes 3-D object-based directional threading and extensions of weighted adaptive lifting (WAL) scheme. The 3-D object-based directional threading, which unifies the concept of temporal motion threading and 2-D spatial directional threading, provides the opportunities to align a series of video object planes to form a 3-D video object and exploit the spatio-temporal correlation inside the 3-D video object. The WAL scheme, which is extended from 2-D frame-based image coding to 3-D object-based video coding, is employed to decompose the 3-D video object into a 3-D multispatio-temporal resolution video object pyramid for object-based scalable video coding. Experimental results show that the proposed 3-D shape-adaptive directional wavelet coding technique consistently outperforms MPEG-4 and other wavelet-based schemes for coding arbitrarily shaped video objects.