Harry and Penelope Seidler House, Modernist residential house in Killara, Sydney, Australia.

The Harry and Penelope Seidler House is a modernist residential building in Killara that extends across four levels connected by a central staircase. The structure follows the natural slope of the land toward a creek and waterfall at the base, with a swimming pool added in the 1970s completing the design.

The house was designed and built by Harry and Penelope Seidler between 1966 and 1967, earning the Wilkinson Award from the Royal Australian Institute of Architects. This recognition confirmed its importance in Australian architectural history.

The house was the Seidlers' own home, and Penelope Seidler, an architect herself, designed it jointly with Harry Seidler and Harry Seidler & Associates; Peter Cussel built it in 1966–67. Its interiors pair Norwegian quartzite floors and Tasmanian oak ceilings with furniture by Marcel Breuer, Eero Saarinen and Charles Eames, architects Seidler had studied under or admired.

The house is a private residence at 13 Kalang Avenue, Killara, and is not open for guided tours or public visits; it is best seen from the street. Its four levels follow the slope down toward the creek and waterfall, so the lower floors sit well below road level. The State Heritage Register listing dates from 20 June 2008.

The house rests on three rows of vertical reinforced white concrete piers that support suspended concrete floors and create open vertical spaces. These innovative supports form a distinctive visual element that emphasizes the floating quality of the structure.