# Initialize SDK

Before initializing the tBTC SDK instance in your project, you need to answer the following questions:

* What Bitcoin network and which tBTC contracts do you plan to interact with?
* Do you want to perform just read-only actions or send transactions as well?

Answering those questions will allow initializing the SDK in the right way. The SDK is prepared to handle common use cases but provides some flexibility as well. This guide explains that in detail.

## Specific guides

{% hint style="info" %}
These guides will show you how to initialize the SDK in mainnet, testnet, crosschain or custom mode.
{% endhint %}

{% content-ref url="/pages/eoNzev0ciRsjBzGE4Wh7" %}
[Ethereum and Bitcoin mainnet](/app-development/tbtc-sdk/guides/initialize-sdk/ethereum-and-bitcoin-mainnet.md)
{% endcontent-ref %}

{% content-ref url="/pages/IyyThGGiDlY4l6D21QDf" %}
[Ethereum and Bitcoin testnet](/app-development/tbtc-sdk/guides/initialize-sdk/ethereum-and-bitcoin-testnet.md)
{% endcontent-ref %}

{% content-ref url="/pages/vzYgTQooYel4wmCBWok2" %}
[Crosschain](/app-development/tbtc-sdk/guides/initialize-sdk/crosschain.md)
{% endcontent-ref %}

{% content-ref url="/pages/qJOdHUlK5bVgW7WuzWGQ" %}
[Custom mode](/app-development/tbtc-sdk/guides/initialize-sdk/custom-mode.md)
{% endcontent-ref %}


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