In an ideal world, a capacitor only provides capacitance. In reality, a physical capacitor behaves like a Series RLC Circuit due to its materials and construction and can be modeled as ideal capacitance in series with ESR and ESL. Below self-resonance, capacitive reactance dominates. At resonance, ESR limits minimum impedance. Above resonance, ESL dominates and the part behaves like an inductor.

Self-resonance occurs where the capacitive and inductive behaviors balance. The actual mounted resonance depends on the complete connection geometry, not only the component datasheet.

Multiple capacitor values broaden the low-impedance range, but their interaction with plane and via inductance can create anti-resonance peaks. A smaller nominal value is not automatically a better high-frequency capacitor if it is placed farther away or connected through a narrow neck. Below are the main parasitic components associated with capacitors and the respective impact and significance on a given circuit.