System-in-Package (SiP) has recently become a significant technology in the semiconductor industry, offering to the consumer applications many new product features without increasing the overall form factor. In this talk, the basic SiP concepts are first discussed, showing difference between SiP and SoC, illustrated by some examples, drawn from real-life cases. The specific challenges are considered from the testing point of view, focussing on the assembled yield and defect level for the packaged SiP. Various bare-die test techniques to find known-good-dies are described including their limitations, followed by two techniques to test the SiP at the system level: functional system test and embedded component test. A brief discussion on future SiP design and test challenges concludes the presentation.