Pippa Middleton has been doing it up big in London promoting her very first book, a party-planning tome titled Celebrate: A Year of Festivities For Families and Friends. While her sister, Kate, didn't show, Pippa spent all of Thursday on the press run at Daunt Books in Chelsea, and looked seriously stylish while doing it. She ran the gamut in a handful of cute looks by designers like Roksanda Ilincic and Markus Lupfer, then finished up her day in Stella McCartney's Mixed-Fabric Sheath Dress ($2,485). While simple, Pippa's look still made a statement — it's a chic workwear look that also manages to look great in a celebratory setting. We think her big sister, the duchess, would definitely approve.