Scalability is a blockchain's ability to handle more transactions as demand grows. Bitcoin processes about 7 transactions per second. Ethereum handles around 15. Visa processes tens of thousands. That gap is the scalability problem. When a chain gets busy, fees rise and users wait. If the chain cannot scale, it cannot serve as a payment network for the world. It becomes a settlement layer for the wealthy.

Solutions fall into two categories. Layer 1 scaling changes the base protocol: bigger blocks, sharding, or faster consensus. Layer 2 scaling builds on top: rollups, sidechains, and state channels. Each approach has trade-offs. Bigger blocks increase throughput but make it harder to run a node, which hurts decentralization. Sharding splits the chain into pieces, which adds complexity and new security assumptions. Rollups move execution off-chain and settle on-chain, which preserves base-layer security but requires bridges. The scalability trilemma says you can optimize for two of three: scalability, security, and decentralization. Every design choice picks a corner.

Scalability approaches

• Bigger blocks — more throughput, fewer nodes
• Sharding — parallel processing, complex coordination
• Rollups — off-chain execution, on-chain settlement
• Sidechains — independent chains with their own consensus

No blockchain scales infinitely. The question is where the bottlenecks move and who bears the cost.