Interstellar nanoparticles, including polycyclic aromatic hydrocarbons (PAHs), are believed to play an important role in modern astrophysics. Mid-infrared emission from PAHs is widely used as a tracer of star formation activity. PAHs is also thought to be a leading carrier behind the long-standing mystery of Diffuse Interstellar Bands (DIBs). In this talk, I will discuss new insights into the crucial importance of interstellar nanoparticles. I will start with a review on anomalous microwave emission (AME) by rapidly spinning nanoparticles, which is a critical challenge for early universe study via cosmic microwave background (CMB) radiation. Then, I will present a new way to tracing magnetic fields via polarized mid-IR emission from PAHs. Finally, I will discuss future perspectives to study interstellar nanoparticles through multiwavelength observations with Square Kilometer Array and ALMA Band 1.